Conservation beyond boundaries

April 7, 2023April 10, 2023 / Graham Appleton / 4 Comments

When an environmental impact assessment concludes that only a small number of shorebirds will be affected by a new airport, because relatively small flocks are counted during field surveys, is there an assumption that the birds encountered are always the same individuals? What if different shorebirds use the same patch of mud at different stages of the tide, at different times of day or in different seasons? How many birds might really be affected?

In a 2023 paper in Animal Conservation, Josh Nightingale and colleagues investigate the movements of colour-marked Black-tailed Godwits, to see how much they fly into, out of and around a Special Protection Area, to work out how well an Environmental Impact Assessments (EIA) might assess the importance of a site that has been scheduled for development. They call for more use to be made of movement data, to assess the total impact of new developments proposed for estuaries and elsewhere.

Impact assessments

The pressures on estuaries have never been greater, as humans turn to them for transport, food, energy and to create land for new developments, such as airports. These muddy havens might be protected by national and international statutes but legally-enforceable conservation designations tend to melt away when there is money to be made, as discussed in Tagus Estuary: for birds or planes?

Developers often argue that they only want to use a small area; taking a bite out of an estuary may seem to affect only 10% (for instance) of a Protected Area – and leave 90%. Counting the birds that use that particular section might show whether this ‘10%’ contains more or fewer birds than expected and indicate whether an unacceptably high proportion of the species for which the Protected Area was designated might be affected. How much more can be learnt if we consider movements that take place within an estuary, the waves of birds that use the estuary in different seasons, the importance of the site within a Flyway and linkages to breeding areas?

Thanks to ringing and colour-ringing, we know that Protected Areas can form networks of sites used by individuals. For example, an islandica Black-tailed Godwit might moult on the Wash (Eastern England), spend the winter on the Tagus (Portugal) and spring in Morecambe Bay (Northwest England). Thousands of limosa Black-tailed Godwits that winter in West Africa spend two months in the Tagus in spring, where they will be seen alongside Grey Plovers from Siberia, Turnstones from Canada and Bar-tailed Godwits from the Arctic regions of Scandinavia. Our knowledge of the strength and complexities of these networks is deepening, still further, thanks to satellite tracking, and the same technology provides the potential to understand more about within-estuary movements too.

Network Analysis

*Josh Nightingale measures a Black-tailed Godwit* *with the Tagus Estuary Ringing Group*

Information on movements of individual birds, generated by ringing, together with the development of methods such as network analysis, provides a framework in which researchers can assess the importance of Protected Areas – or threatened parts of Protected Areas. Network analysis is the study of connections. In this context, a network is simply a collection of sites, dubbed nodes, linked by connections known as edges, which may have varying directions or strengths.

In pictorial terms, ‘thicker’ edges indicate that more birds connect two nodes. When assessing connectivity, the researchers considered the number of other nodes each node is linked to and the variety of pathways between nodes.

Despite being powerful and flexible, network analysis is currently used less by conservation practitioners than by academics, and much of their work is at landscape- or regional-scales. In a 2023 paper, Josh Nightingale and his colleagues adjust the focus, to see how network analysis might explain what is happening within and around a Protected Area – information that is valuable when trying to assess conservation implications of planning decisions. They use movement data to reveal the range of sites used by individuals, and thus the susceptibility of those individuals to a local development.

Network analyses can reveal which sites are most important to population-level connectivity, or the impact on connectivity of losing one or more sites. These results can be combined, to calculate the ‘impact footprint’: how many individuals use the impacted area and how do their movements connect with neighbouring sites (inside or outside the Protected Area). By representing movements between sites in a network, practitioners can gain a more accurate picture of how the effects of a localized impact may be felt at connected sites. This information can then be used to determine whether populations or habitats are impacted, and thus inform policy decisions.

Applying a Network Analysis framework to the Tagus

*Black-tailed Godwits feeding along the shoreline of a built-up area* *in the Tagus estuary*

The Tagus Estuary, on whose banks Lisbon sits, is Portugal’s largest wetland and the country’s most important site for many waterbird species. Part of the estuary is designated under the EU Birds Directive as a Special Protection Area (SPA), with a smaller Ramsar Site at its core. The SPA excludes several of the estuary’s high-tide roosts, which consequently lack legal protection and are vulnerable to development, erosion and other threats.

The Portuguese Environment Agency has issued an Environmental Licence, approving plans to construct an international airport in the heart of the Tagus estuary, on a site overlapping part of the SPA. The Environmental Impact Assessment (EIA), conducted for the development, considers the main threat to bird conservation to be noise disturbance, with an aeroplane taking off or landing every 2.5 minutes and flying at low altitude (<200 m) over the SPA (see article by José Alves in Wader Study). Such disturbance can cause birds to take flight, with consequent increases in daily energy expenditure. The effect can be seen even when the airport has been operational for decades (van der Kolk et al). Airport-related disturbance close to wetlands has been shown to influence the distribution of waterbird communities (Celdrán & Aymerich).

The predicted impact of the Montijo airport development varies, depending upon the threshold of noise sensitivity assumed. Although it has been shown that waterbirds alter their behaviour when subjected to noises above 50 dB(A) (see Wright et al., the study used as a reference for the EIA), the Environmental Licence for Montijo Airport only considers relevant areas impacted by over 65 dB(A). Crucially, movements of birds within, to or from the Protected Area were not considered.

To assess how network analysis might explain the real impact of the airport, Josh Nightingale and his colleagues focused on the Black-tailed Godwit, a species for which the Tagus SPA had been designated and for which a large amount of colour-ring data was available. They wanted to answer these questions:

How much of the local godwit population is protected by the Protected Area during the year, and how much does this overlap with the area to be impacted by development?
How much of the Tagus is used by birds from the Protected Area, and by birds from the area that would be affected by low-flying aircraft?
Which sites are linked most closely to others and how might the predicted development weaken connections between sites across the Tagus estuary?

Assembling the data sets

*Black-tailed Godwit ringed as an adult in Iceland*

Islandica Black-tailed Godwits have been intensively studied since 1993, when the first birds were colour-ringed. The datasets used in these analyses comprise sightings of birds ringed in Iceland, on the Wash (Eastern England) and in the Tagus (Portugal). Sightings of these colour-ringed birds have been reported by thousands of observers across the whole range of the subspecies. To get a flavour of the importance of these reports (and the dedication of birdwatchers) read Godwits and Godwiteers.

Within the Tagus Estuary, the focus was on marked birds reported between 1st January 2000 and 1st July 2020. Observations were recorded at 30 sites that were visited at least once during early and late winter, and more frequently since October 2006. To reduce the potential risk of observation error, only sites at which an individual was recorded at least twice during its lifetime were assigned to that individual.

To assess site-level noise-exposure that birds might experience, Josh Nightingale and colleagues analysed their data based on the areas in which godwits might encounter noise levels of 55 dB(A) and 65 dB(A). Full methods used in the network analysis are given in the paper.

Impacts on Black-tailed Godwits

Individual Black-tailed Godwit are conservative in their habits. At a Flyway scale, they typically use only four or five different sites per year, with this annual schedule remaining constant over up to twenty years (as discussed in Generational Change). Josh Nightingale found similar consistencies within the Tagus Estuary. Most of the 693 individually-tracked godwits were found at six or fewer sites (of the thirty available), even when observed for a decade or more. 82.8% of individual godwits used sites inside the SPA and 67.7% used sites outside the SPA. There was seasonal variation in the protection footprint of the SPA, which was three times as important in October-December as it was in January-March

In the early part of the winter, islandica Black-tailed Godwits are most likely to be found feeding on the estuary itself, with many moving to inland feeding sites, particularly rice fields, in January to March. Much of the area that would be impacted by the noise from aircraft is over the estuary so it is not surprising that the impact footprint is greater in October to December, when disturbance is estimated to affect 68.3% of the godwits, if a threshold of 55 DB(A) is used, or 40.7% based on 65 dB(A).

*Godwits on the intertidal flats of the Tagus estuary*

When the researchers considered individual movements within the same winter, they found that birds from within the Protected Area visited 14 out of 17 of the sites that lie outside the Protected Area. A flock of roosting or feeding birds seen well outside the SPA is very likely to include birds that also feed in the SPA. There were similar levels of connectivity from unimpacted sites across the estuary to the 55 dB(A) impact zone. The most centrally connected site, the Giganta rice fields, is outside the SPA but within the 55 dB(A) affected area – hence unprotected and highly impacted.

*Take off! Part of a flock of thousands of Black-tailed Godwits taking off from a rice field* *in the Tagus estuary*

Turning the focus to the area of the estuary that will be most impacted by aircraft noise, the researchers found that 68% of islandica Black-tailed Godwits in the Tagus will be affected. This is higher than an estimate of between 0.5% to 5.5% that was quoted in the EIA. The lower estimate is based on a 65 dB(A) threshold, rather than 55 dB(A), uses old counts and does not consider bird movements. This implies that the effect of the airport on Black-tailed Godwits will be twenty times as large as considered in planning decisions. And this discrepancy is just for one of the species for which the Tagus is designated as an SPA and Ramsar Site.

The paper contains a detailed analysis of how the protected network would be degraded by the new airport, through loss of key sites and by taking out edges that link current nodes that will be affected by disturbance. Overlaying the 55 dB(A) on the current Tagus network has the potential to reduce connectivity between sites by nearly 30%, effectively partially blocking the free flow of birds around the estuary.

Conservation implications

The footprint approach developed by Josh Nightingale is really neat. For the Tagus, it shows that over half of the colour-marked Black-tailed Godwits use sites outside the Special Protection Area, as currently defined, and that the majority of the most important sites that provide connectivity across the estuary are also unprotected.

Using Black-tailed Godwits as an example, the research team show that the EIA may have underestimated the impact of the airport by a factor of about 20. When disturbed by aircraft or scared off to reduce strike risk, more energy will be expended and some birds may permanently desert key feeding or roosting areas. Research elsewhere has shown that displacements can have temporary and even long-term effects on the survival rates of affected individuals.

To quote from the paper, “Protected Areas are a critically important conservation tool to protect populations, especially as ranges shift in response to climate change. To secure the integrity of PAs and the populations they support, we need to be able to accurately assess the impacts of developments inside and outside PA boundaries. Animal-tracking data offer exciting and feasible opportunities to assess PAs’ contributions to protecting populations of mobile species and the potential for adverse effects of external developments on PA integrity.”

Conservation beyond Boundaries: Using animal movement networks in Protected Area assessment. Josh Nightingale, Jennifer A. Gill, Böðvar Þórisson, Peter M. Potts, Tómas G. Gunnarsson & José A. Alves. Animal Conservation. Doi: 10.1111/acv.12868.

*Black-tailed Godwits moving to roost on the saltmarsh, as the tide covers the mud*

WaderTales blogs are written by Graham Appleton (@GrahamFAppleton) to celebrate waders and wader research. Many of the articles are based on published papers, with the aim of making shorebird science available to a broader audience.

Why count shorebirds? A tale from Portugal

February 14, 2023February 14, 2023 / Graham Appleton / 1 Comment

The Sado Estuary is one of Portugal’s most important wetlands – a key link in the chain of sites connecting Africa and the Arctic, on the East Atlantic Flyway. In a paper in Waterbirds, João Belo and colleagues analyse changes in numbers of waders wintering in this estuary over the period 2010 to 2019, with a focus on roost sites. These results are interpreted in regional and flyway contexts. The team find serious declines in numbers of Avocet, Dunlin and Ringed Plover.

Lost roost sites

The Sado Estuary became a nature reserve in 1980 and has since been classified as a Ramsar Site, a Special Protection Area (SPA – Natura 2000) and an Important Bird and Biodiversity Area. The Estuary lies about 30 km south of the much larger and more famous Tagus (or Tejo) Estuary, which is threatened by a new international airport (see Tagus Estuary: for birds or planes?). A suggestion that the Sado could provide mitigation habitat for damage done to the Tagus prompted scientists from the Universities of Aveiro and Lisbon to review the current state of the estuary.

João Belo and his colleagues used monthly data from a programme of wader surveys, conducted largely by volunteer birdwatchers. These took place between January 2010 and December 2019. Roosting birds were counted at high tide along the northern shores of the Sado estuary and any habitat changes were noted.

During the ten-year survey period, 21% of the available high-tide roost area was lost. These changes were associated with the commercial abandonment of saltpans (with consequent increases in vegetation) and the conversion of others for fish farming (often with netting, to keep out fish-eating birds).

Results of the survey

In their paper, João Belo and colleagues focused on total numbers of waders and counts of the six most commonly-encountered species: Avocet, Dunlin, Black-tailed Godwit, Redshank, Ringed Plover and Grey Plover. They compared winter (Dec, Jan and Feb) counts in 2019 with those from 2010. This is when peak numbers of Avocet, Redshank and Grey Plover occur. Higher counts of Dunlin are made in spring, as schinzii birds returned from Africa, with peak counts of Black-tailed Godwit and Ringed Plover occurring in autumn.

The key findings are:

There was a strong decrease in the overall number of waders wintering in the Sado Estuary. This trend is mostly driven by steep declines in three of the six most abundant species: Avocet, Dunlin and Ringed Plover.
Avocet numbers were 42% lower in 2019 than they had been in 2010.
Dunlin numbers dropped by over half, with 2019 counts being only 47% of those in 2010. These are mostly dunlin of the alpina subspeciesthat breed between Northern Scandinavia and Siberia.
Ringed Plover numbers dropped by 23% between 2010 and 2019.
Redshank increased significantly between 2010 and 2019, while the population of Grey Plover was relatively stable, and it was not possible to derive a population trend for Black-tailed Godwit.

It is interesting to look at these patterns alongside data collected in Britain & Ireland, over the same period. As discussed in Do population estimates matter? and Ireland’s wintering waders, there have been major changes in wader numbers, with most species currently in decline.

*At the same time that Avocet numbers have dropped on the Sado Estuary they have rocketed in the UK (here seen on the Humber Estuary)*

Winter Avocet numbers have increased massively in Britain & Ireland. It is possible that young birds are more easily able to settle in these northern areas, now that winter temperatures are generally warmer. Declines in Portugal may reflect a northwards shift of the winter population, driven by new generations of birds.
Numbers of Ringed Plovers in Britain & Ireland did not change over the period 2010 to 2019 but had dropped a lot in the preceding twenty years.
For Dunlin, the size of the declines in Britain & Ireland are consistent with those on the Sado. It has been suggested that more young birds might be settling in areas such as the Wadden Sea, closer to Siberian breeding areas, something that may have become more possible given the reduced intensity and occurrence of freezing conditions along the east coast of the North Sea.

Regional and Flyway patterns

As discussed in the blog Interpreting changing wader counts, based on research led by Verónica Méndez, local changes in numbers are usually reflective of broader changes in population levels. Individual waders are unlikely to seek alternative wintering sites unless habitat is removed, so birds do not re-assort themselves into the ‘best’ areas when population levels decrease. Instead, there is general thinning out across all sites as populations decline. In this context, it is unsurprising that the trends in the Sado Estuary are similar to those found elsewhere in Portugal and in other Western European wintering areas.

Looking forwards

The survey data collected between 2010 and 2019 form a useful backdrop against which to monitor what might happen when (or perhaps if) a new international airport is constructed within the nearby Tagus Estuary. If some birds are displaced to the Sado, increases in numbers might be expected.

Displacement is not cost-free, as has been shown in a well-studied population of Redshanks on the Severn Estuary in Wales. When Cardiff Bay was permanently flooded, as part of a major redevelopment, colour-marked Redshank dispersed to sites up to 19 km away. Adult birds that moved to new sites had difficulty maintaining body condition in the first winter following the closure of Cardiff Bay, unlike the Redshank that were already living in these sites. Their survival rates in subsequent winters continued to be lower than for ‘local’ birds, indicating longer-term effects than might have been predicted.

These three papers are essential reading for anyone interested in the consequences of displacements caused by development projects.

Burton, N.H.K. 2000. Winter site-fidelity and survival of Redshank at Cardiff, South Wales. Bird Study 47: 102–112.
Burton, N.H.K. & Armitage, M.J.S. 2005. Differences in the diurnal and nocturnal use of intertidal feeding grounds by Redshank. Bird Study 52: 120-128.
Burton, N.H.K., Rehfisch, M.M., Clark, N.A. & Dodd, S.G. 2006. Impacts of sudden winter habitat loss on the body condition and survival of Redshank. Journal of Applied Ecology 43: 464-473

Given that the Sado has multiple conservation designations, including as a Ramsar site, and that this study has shown a clear loss of available roosting areas, perhaps it is time to identify a high-tide refuge that can be fully protected and managed in ways which create a range of suitable habitats for use by long-legged and short-legged waders. A nature reserve such as this has a potential to attract birdwatchers too, with prospective increased income from tourism.

Sado International

Curlews don’t get a mention in this paper but the The Sado provides a neat link to a 2022 blog, A Norfolk Curlew’s Summer. This tale focuses on ‘Bowie’, a male Curlew that breeds in Breckland (Eastern England) and has been tracked to The Sado Estuary. In the blog, Bowie’s story stops in The Tagus but he subsequently headed further south to The Sado, where he spent the winter. At the time of writing (13 Feb 2023) he is still there but hopefully he will heading north soon.

The Sado is not only important in the winter, of course. As mentioned earlier, it is a spring stop-over for birds such as schinzii Dunlin, heading north from Africa to Siberia, and a moulting/staging site for waders heading south in late summer. Tracking and colour-ringing are telling more of these stories, with links to countries as far north as Canada and Siberia and as far south as South Africa.

*The overgrown embankments within the former saltpans no longer provide suitable roosting sites for waders*

Keep counting

The Sado story could not have been written without the work of volunteer counters who collect monthly data during the winter months, on the Sado Estuary, across Portugal and on the wider East Atlantic Flyway. These monitoring efforts are essential when attempting to track changes in wader populations, especially when extra information can indicate links to habitat changes, as is the case in the Sado. The international picture is painted using Flyway information generated using January counts that are developed by the Institute for Nature Conservation and Forests (ICNF).

Here is a link to the paper:

Synchronous declines of wintering waders and high-tide roost area in a temperate estuary: results of a 10-year monitoring programme. João R. Belo, Maria P. Dias, João Jara, Amélia Almeida, Frederico Morais, Carlos Silva, Joaquim Valadeiro & José A. Alves. Waterbirds. doi.org/10.1675/063.045.0204

*Birdwatchers that volunteered to survey roost-sites gather for a team photo*

Curlew nest survival

January 4, 2023 / Graham Appleton / 3 Comments

The Eurasian Curlew is designated as ‘Near-Threatened’ by IUCN/BirdLife. It is Red-listed in the UK, largely due to a rapid decline in breeding numbers. In this context, the fact that there are a few pink squares (indicating increased numbers) on the map showing breeding abundance change between 1988-91 and 2008-11 looks encouraging.

Why are Curlew doing relatively well in some areas and might these conditions be replicated? In a 2023 paper in IBIS, Harry Ewing examines how nest survival varies within Breckland, the area indicated by a red circle on the map alongside.

Curlew problems

The landscape changes associated with declining numbers of British breeding Curlew were reviewed in a 2017 paper by Samantha Franks and colleagues and summarised in the WaderTales blog Curlews can’t wait for a treatment plan. In 2020, Aonghais Cook et al analysed annual survival rates of Curlews in Britain and concluded that these were remarkably high, strongly suggesting that productivity is the main problem, as discussed in More Curlew chicks needed. Harry Ewing, a PhD student at the University of East Anglia, has been studying Curlews breeding in Breckland since 2019, in the hope that he might find answers to the question “Are there circumstances in which England’s lowland Curlew breed successfully?” The answer has implications for Curlews in other areas.

Targeting help for Curlew

Visitors to UK wetland nature reserves are becoming used to seeing fenced areas, in which species such as Avocet and Lapwing can nest relatively successfully, out of the reach of mammalian predators. These fences tend to shine a spotlight on the role of mammalian predation in wader declines but this is only part of the problem.

Landscapes used by ground-nesting birds have been massively changed by agricultural intensification and afforestation, which may make nests more vulnerable to predation. Additionally, human-induced climate change is rapidly altering environmental conditions. It’s hard to hide a nest if the grass won’t grow and difficult for chicks to find insects in a drought.

A set of tools is available to those managing land for semi-colonial waders in lowland wet grasslands (see Tool-kit for wader conservation). For Curlew breeding at much lower densities across human-modified landscapes, such as farmland, conservation is more challenging. In his IBIS paper, Harry Ewing quantifies variation in Curlew nest survival, in order to explore how management could be targeted to boost this key component of breeding productivity. Up to 80 pairs of Curlew were monitored annually between 2019 and 2021, in eight locations across Breckland, eastern England, an area in which nesting densities ranged from less than one to more than seven pairs per km².

Breckland Curlew

The Brecklands of East Anglia have been shaped by humans for millennia. In their current form they comprise intensive farmland, commercial forestry plantations, and military bases and training areas, with pockets of land managed for the distinctive flora and fauna communities that used to be widespread across dry, grazed heath and grasslands. Curlew in Breckland can be found nesting alongside runways, within sugar-beet fields and on nature-reserves.

In this study, pairs were monitored across a range of sites and habitats, including arable farmland, grassland, cleared forest, a military training area and an RAF base. The eight study sites were dominated by arable fields or semi-natural grassland, which is maintained by mowing or livestock grazing. Public access was restricted and some areas within grassland sites were enclosed by fencing. None of the fences were designed to protect breeding waders but their presence around military bases and to reduce grazing pressure in forests potentially provide benefits for Curlew, by reducing fox encounters.

Most of the fieldwork was conducted in 2019 and 2021, when 55 and 69 nesting attempts were followed. Curlew nests can be hard work to locate, and anyone who has ever studied breeding Curlew will be impressed by these numbers! The 2020 season started late, due to Covid-19 restrictions, but added another 12 nests.

The location of each nest was recorded with a GPS device, an iButton temperature logger was deployed in the nest lining, in order to capture the timing of nest failures, and hatching dates were predicted from the weights and measurements of eggs (more details in the paper). Regular monitoring and more frequent visits close to hatch date provided information on nest outcomes. Nest concealment was recorded on the day on which each nest was located, by measuring the height of vegetation around the nest.

*Sugar-beet provides good cover, as the plants start to grow*

Assessing nesting success

Curlew breed in a wide range of densities across the Breckland study area. Six sites held between 0.17 and 0.72 pairs per km², while two other hosted densities of between 3.3 and 7.4 pairs per km². Nearly half of the probable or confirmed breeding pairs monitored annually were on the latter two sites, despite the fact that between them they only accounted for 5% of the study area.

A total of 136 Curlew nests were monitored across Breckland over the three summers, with the majority being found in unfenced grassland areas. 185 chicks hatched from 52 nests and 84 nests failed. Predation accounted for 86% of nest failures, with three nests failing during laying, one being trampled by cattle and five being lost during farming activities.

The key result in the paper is that hatching success was not high enough, in any habitat, in any year. There was some variation between sites but the mean probability of surviving incubation, for all hatched or predated nests was about 0.25, which is well below the estimated requirement for sustainability of a population.

Nest survival was similar in unfenced grassland, fenced grassland, arable fields and ground-disturbance plots within grassland, and across levels of nest concealment, so the spatial variation in nest survival was not the result of variation in management conditions or of nest concealment between sites. Only nine nests were found in fenced areas, making it unlikely that any positive effect of fencing could have been detected.

For nests for which data from temperature-loggers were available, it was possible to infer that 36 out of 44 predation events took place during the (short) nocturnal period, the time when foxes are most active.

Implications for Curlew conservation

It would have been great if Harry had been able to find a prescription for Curlew nesting success, by identifying a set of circumstances that delivered plenty of chicks. The fact that this was not possible, despite monitoring a large number of pairs, in a variety of habitats and across a broad density gradient, emphasises how hard it is going to be to preserve Curlew as a breeding species in England. Head-starting (raising chicks in captivity) may be able to give a temporary boost to numbers (see Will head-starting work for Curlew?) but these new recruits need to be able to breed successfully if local populations are going to be sustainable.

As the great majority (86%) of nests failed because of predation, boosting hatching rates of Curlew nests is likely to require actions to reduce mammalian predator impact across large areas of Breckland. It is much harder to help thinly-spread Curlew than semi-colonial Lapwing.

A conservation tool that is commonly deployed to reduce predation on ground-nesting birds’ nests is predator-exclusion fencing. Fences have the potential to double wader hatching rates in species such as Lapwing (Malpas et al. 2013) and it seems likely that they could also be effective at boosting Curlew nest survival, if provided at an appropriate scale.

In Breckland, fences were not deployed to protect Curlew nests A small number of pairs nested within fenced areas but too few to detect an observable effect of fencing on nest survival. Increasing the number of nests enclosed by predator fencing in Breckland could potentially be achieved by deploying temporary electric fencing to protect individual nests but the substantial annual efforts required to locate nests and erect and maintain fences make this impractical, especially in areas where Curlew breed at very low densities.

The authors suggest that targeted deployment of fencing could potentially be effective if focused on ground-disturbance plots within grassland (see graphic below). These areas were originally developed for Stone-curlew but are often used by nesting Curlew, as described in a paper by Natalie Zielonka et al and summarised in Curlews and foxes in East Anglia. Plot-level fencing could be deployed at the start of the season, without the need to locate nests, and may benefit other ground-nesting species such as Lapwing. Unfortunately, these plots currently only support between four and seven breeding pairs of Curlew in the study area, suggesting only a modest potential increase in chick production.

Another alternative might be to erect permanent barrier fences along the boundaries of sites supporting high densities of nesting Curlew. Fencing the combined boundary length of the eight Breckland study sites that between them support about 80 pairs would require 185 km of fencing, which would be prohibitively expensive. However, given that nearly half of these pairs were breeding in just two of those sites, with a combined boundary length of only 14 km, perhaps this is where efforts might be focused? Assuming such fences would be as effective as for other waders, enclosing these two high-density sites with permanent barrier fencing could potentially boost the total number of chicks hatched in Breckland by about 90 chicks per year. It would be interesting to calculate whether this might be a more cost-effective way of producing fledged chicks than head-starting.

To sustainably maintain and recover Curlew populations in the wider landscape, in Breckland and elsewhere across the breeding range, actions outwith fenced areas are likely to be required. Lethal control of foxes, the main mammalian nest predator in the region, occurs across much of the Breckland study area and it would be useful to know how effective it is at limiting nest predation levels. This means learning more about predation, predator behaviour and control measures.

Across England, regional stakeholder networks are going to be important. Curlew territories are large and pairs move between habitats, implying a need to integrate evidence-based, Curlew-friendly policies into large-scale agri-environment schemes. Harry Ewing and his co-authors suggest that the next steps are to work with stakeholders to trial management actions for Curlew (e.g., fencing, head-starting and predator control). Actions to boost nest survival will need to be targeted in areas that contain suitable habitat to support chick growth and survival. Further research is required to understand the land management actions that can create and maintain such conditions at different scales.

To find out more

This blog focuses on the first paper from Harry Ewing’s thesis, undertaken by the University of East Anglia on a Natural Environment Research Council CASE studentship, as part of the EnvEast DTP. It was part funded by the British Trust of Ornithology, with support from RSPB and via a Defence Infrastructure Organisation Environmental Stewardship grant.

Nest survival of threatened Eurasian Curlew (Numenius arquata) breeding at low densities across a human-modified landscape. Harry Ewing, Samantha Franks, Jennifer Smart, Niall Burton & Jennifer A Gill. IBIS. doi.org/10.1111/ibi.13180

WaderTales blogs in 2022

December 22, 2022January 22, 2023 / Graham Appleton / 1 Comment

Here are brief summaries of the sixteen WaderTales blogs that were published in 2022. I have grouped the blogs into sections; problems with trees, more research from Iceland, Curlews, news from the East Asian-Australasian Flyway, tracking and updates.

As ever, I am grateful to the authors of the papers that underpin the blogs; they have worked with me to make sure that I get the stories right!

Problems with Trees

Everyone agrees that forests are immensely important to the future of the planet. Keeping the trees we have is obviously much better than planting new forests, especially if rich habitats that are home to breeding waders are turned into single-species blocks of trees, in dubious plans to lock up carbon.

Hiding in the trees. In the second paper from her PhD, Triin Kaasiku looks at the breeding success of Estonian coastal waders that nest at different distances from woodland. Keep away from the trees describes these ‘edge effects’. In a part of the world where waders are in diminishingly short supply, hatching success is six time as high in open areas as in areas that are within one kilometre of forest edge. The Baltic coast used to be a haven for species such as Curlew and Dunlin but reduced grazing and forestry plantations have provided hiding places for predators. Alongside increased predation, breeding waders are also having to contend with an increasing numbers of nest inundations, arising from summer storms.

Conflict with forestry. By mapping distributions of breeding waders in the vicinity of Icelandic forests, Aldís Pálsdóttir has shown that new plantations have a massive effect on distributions. In lowland Iceland, the most vulnerable species appear to be Dunlin and Oystercatcher, followed by Whimbrel, Black-tailed Godwit and Golden Plover. Aldís and her fellow authors argue that Iceland’s waders need a strategic forestry plan. They estimate that recently-planted woodland and forests have already removed the breeding territories of tens of thousands of waders.

Icelandic Research

WaderTales blogs started out as a promotional vehicle for research findings from Iceland. This explains why there are so many stories featuring Black-tailed Godwits, for instance, in the full catalogue of blogs. Iceland is hugely important, in the context of the East Atlantic Flyway, with 75% of Europe’s breeding Whimbrel and about half of the Golden Plover and Dunlin.

Power-line problems. We have seen huge changes in Iceland, since we first visited in 2000, but how are these affecting shorebirds? In the first paper from her PhD (Effects of land conversion in sub-arctic landscapes on densities of ground-nesting birds), Aldís Pálsdóttir investigated how distributions of breeding waders are affected by power-lines. She discovered significantly depressed numbers several hundred metres from the transmission lines, with Whimbrel and Redshank being the most obviously impacted. Her results are written up as Power-lines and breeding waders. With an increasing global reliance on electricity, these are important findings for planners.

Oystercatcher: mixed marriages. Research by Verónica Méndez and the Icelandic Oystercatcher team looks at the costs and benefits of being migrants. In the 2022 paper they investigate the timing and success of breeding attempts by resident, migratory and mixed (resident/migratory) pairs. The results are summarised in When mates behave differently.

A Whimbrel’s year. How easy is it for waders to make up for lost time if they experience delays during breeding, wintering or migration periods? For instance, what happens if a pair of Whimbrel loses a first clutch and a successful, late breeding attempt delays departure from Iceland? Is there the flexibility to make up for lost time during a west-African winter? Some answers are provided in a paper by Camilo Carneiro et al in The American Naturalist and summarised in A Whimbrel’s year.

Personal appreciation of Whimbrel. On 27 April, Jenny Gill and I were at Eyrarbakki, on the south coast of Iceland. As we watched, small groups of Whimbrel were coming in off the sea. Others were resting on the seaweed-covered rocks, a few were feeding and some flew straight by. Watching waders arrive in Iceland is always magical but, from sightings of satellite-tagged Whimbrel, we could be pretty sure that these tired birds had just completed five-day, direct flights from west Africa. I could not wait to get back to base and to share our observations in Whimbrels arrive in Iceland.

More about Curlew

By the end of 2021 there were nine Curlew blogs in the WaderTales catalogue, with three more added in 2022. These all relate to Eurasian Curlew but much of the research may well be relevant to other members of the family.

Curlew hunting. Curlew hunting stopped in Great Britain in 1982, when the declining wintering population received protection under the new Wildlife & Countryside Act. A fascinating paper by Ian Woodward and BTO colleagues teases apart the positive effects of the cessation of shooting and more benign winter weather. It is summarised as Curlew: after the hunting stopped.

I am old enough to remember when Curlew were hunted in East Anglia. The pâté made from autumn-shot birds is reputed to have been very tasty; I recall Clive Minton getting back in his land-rover and reporting that he had been offered some, when asking for permission to cannon-net Curlew on a Norfolk land-owner’s estate.

Tale of a Norfolk Curlew. Tracking information can provide some amazing detail about the lives of individual waders. When Harry Ewing, Sam Franks, Nigel Clark and others caught a small number of birds, on 2 April, just before the start of the breeding season, they had no idea that Bowie’s movements would reveal how stoats and forest fires could ruin his summer – but that’s only part of the story in A Norfolk Curlew’s summer.

Captive-reared Curlew. There is no doubt that England’s Curlew are in trouble, with far too few chicks making it through to fledging. While conservation scientists try to work out how best to improve breeding conditions, might head-staring (captive rearing) give populations a temporary boost? What is being learnt by teams in different parts of England – particularly through tracking work in Norfolk? Will head-starting work for Curlew?

East Asian-Australasian Flyway

Three of the sixteen blogs of 2022 focus on research on the East Asian-Australasian Flyway.

Australian stock-take. One of the great joys of writing WaderTales blogs is that I get to ‘visit’ the flyways of the world without having to burn carbon. How many shorebirds use the East Asian-Australasian Flyway? is a flyway-wide stock-take of the waders that visit Australia and New Zealand, led by Birgita Hansen. It is shocking that a flock of 350 Far-eastern Curlew now constitutes 1% of the global population and that the population of Curlew Sandpipers has halved in double-quick time, but the key strength of the paper is the clear explanation of a methodology that can be used in the future, to monitor changes in numbers.

Losing feeding areas in the Yellow Sea. Previous blogs have talked about the problems faced by waders on the East Asian-Australasian Flyway. So What happens when the mud disappears? In a thought-provoking paper in Biological Conservation, Xiaodan Wang and colleagues consider how assemblages of waders have changed, as available habitat has been lost on this flyway. Their results suggest that conservation of these migratory shorebirds will depend upon lots of local initiatives.

Chick vocalisation. Big analyses of data sets are very important but it’s lovely when you learn more about the natural history of species that birdwatchers know well. In Australia, Kristal Kostoglou recorded the calls of the chicks of Red-capped Plovers and Southern Masked Lapwings, that were being ringed and measured in the hand. In Chick squeaks I describe how calls get deeper with age, which is not surprising, but that the calls of males and females can become distinguishable from a very early age. Male Red-capped Plover chicks are more demanding than their sisters!

Tracking stories

This is such an exciting time to be writing about shorebirds, thanks to technologies that enable us to watch individual birds as they cross the globe or just move around our estuaries. The two blogs in this section illustrate research findings at both of these ends of the scale – Hudsonian Godwits crossing the Pacific and Black-tailed Godwits taking advantage of French hunters’ ponds – once the shooting season has closed.

Trans-oceanic migration. There have been several recent wader papers that interpret data obtained from birds when on migration. One of the interesting questions being asked is, “Do shorebirds account for wind displacement continuously or correct for drift later?”. Navigating a vast ocean summarises Jenny Linscott’s work on Hudsonian Godwits, as they cross the Pacific Ocean and then the Gulf of Mexico, on their way from Chile to Alaska. She and her fellow authors show that flocks make continuous adjustments, demonstrating that birds ‘know where they are’ and giving them the ability to fly extremely long distances without running out of energy. There’s some clever maths too!

French Black-tailed Godwits. Species such as Dunlin and Knot are well-served by conservation measures that aim to protect estuaries but the same is not necessarily true for Black-tailed Godwits. In a 2022 paper in the journal Wader Study, Clément Jourdan and colleagues describe the movements of ten tagged Black-tailed Godwits, showing how much time they spend on poorly-protected inland sites and how the species’ use of these habitats changes over the seasons. The work is summarised in Inland feeding by coastal godwits.

Updates and Wales

I try to keep blogs up-to-date, so new additions will appear at the end of old stores when new trend data appear or if there is something extra to say which does not make a whole blog. The Spoon-billed Sandpiper tale from 2020 is an excellent example of a blog that keeps growing. In December, I took the opportunity afforded by the publication of the latest Birds of Conservation Concern in Wales to refresh the 2017 blog about Welsh waders. The other refresh turned into a separate blog, when I marked the publication of the BTO book Into the Red. Sandwiched in the middle is a tale about Welsh Oystercatchers.

The waders of Wales. From winter beaches to summer moorland and woodland, Wales provides essential habitats for waders. The blog Wales: a special place for waders was originally written in 2017, to bring together WaderTales stories that were of particular relevance to Welsh birdwatchers. The publication of Birds of Conservation Concern Wales 4, in 2022, created the perfect excuse for a revamp. The first part of the blog focuses on BoCCW4. This is followed by updated sections about the birds that spend winter in Wales, pass through in spring and autumn, and breed in the country.

Welsh Oystercatchers. In this blog, we learn how flexible Oystercatchers can be in response to changes in their food supply. Katharine Bowgen has brought together long-term data collected by wader ringers and WeBS counters, and added in annual assessments of cockle stocks on the Burry Inlet (South Wales) to tell her story. This paper has a particular resonance, as I remember teaching students about the Burry Inlet Oystercatcher controversy of the 1970s, when complaints from shellfishers led to the deaths of thousands of birds. We understand more about the relationship between shellfish stocks and bird numbers now and this paper makes a strong case for the protection of networks of sites, so that individuals have alternatives when needed. What happens when Oystercatchers can’t find food?

Into the Red. To support a BTO initiative to raise money for the Trust’s science and to support the UK Rare Breeding Birds Panel, I was pleased to write the blog UK Waders: “into the red”. It features the eleven species that find themselves on the list. Some won’t surprise people – the Eurasian Curlew is in trouble everywhere – but why are Dunlin and Purple Sandpiper on the list? The book is a wonderful mixture of words and art, including the lovely Lapwing picture by Jo Wright at the head of this blog.

Blogs from previous years

WaderTales blogs in 2021

WaderTales blogs in 2020

WaderTales blogs in 2019

WaderTales blogs in 2018

WaderTales blogs in 2017

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research. Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.The intention is to add one or two new blogs each month. You can sign up to receive an e-mail notification when a new one is published. There’s a full list of blogs here.

Inland feeding by coastal godwits

November 10, 2022 / Graham Appleton / 2 Comments

Species such as Dunlin and Knot are well-served by conservation measures that aim to protect estuaries but the same is not necessarily true for Black-tailed Godwits. In a 2022 paper in the journal Wader Study, Clément Jourdan and colleagues describe the movements of ten tagged Black-tailed Godwits, showing how much time they spend on poorly-protected inland sites and how the species’ use of these habitats changes over the seasons.

Mobile Black-tailed Godwits

Large numbers of Black-tailed Godwits can be found along the Atlantic coast of France, comprising birds from the booming islandica race and others from the struggling limosa race, with proportions varying throughout year. Some limosa breed in France and head to Africa in autumn but the numbers of this subspecies are dwarfed in autumn and spring, when limosa from the Netherlands and neighbouring countries stop off, to top up their fuel supplies for migration. Adult islandica birds from June/July to April/May and some young islandica stay in France during the summer months too.

This mix of the two races, one of which is increasing (islandica: see From local warming to range expansion) and the other of which is in severe decline (limosa: see Dutch Black-tailed Godwits down by nearly 75%) creates conservation challenges. Hunting of waders is still popular in France and decisions as to which species are legally shot need to be evidence based. Do limosa and islandica mix or are there times of year and circumstances when hunters can be pretty sure that they are targeting only islandica? For the moment, there is a temporary suspension of Black-tailed Godwit (and Curlew) from the quarry list (see Black-tailed Godwit and Curlew in France) while more evidence is collected. Set against this background, it is really important to understanding habitat use by both islandica and limosa.

*Mist nets set to catch Black-tailed Godwits*

Wintering islandica

Icelandic Black-tailed Godwits return to France from June onwards and the last birds do not leave again until the start of May. By analysing the movements of 10 wintering islandica Black-tailed Godwits, using GPS-telemetry, Clément Jourdan and colleagues gained insights into the varied ways in which birds spend their time during this non-breeding period. Although it might look as if Black-tailed Godwits have a wide range of sites at their disposal, each individual only made use of a limited number of options during the course of a winter. The tagged birds moved around at both small and large spatial scales, on tidal and/or daily cycles, and changed their patterns with the seasons.

It was already known that islandica Black-tailed Godwits in France use bare mudflats or seagrass during the autumn, with some individuals using grasslands during the winter, and that most birds migrate to The Netherlands or eastern UK in spring, where they forage primarily on grasslands. This northwards movement, especially to The Netherlands, puts birds in pole position for the flight to Iceland (see Overtaking on migration).

Studies of energy intake rates in godwits feeding on mudflats and grasslands in Eastern England suggested that birds move to grasslands when estuarine food supplies are no longer sufficient to fulfil their energy requirements, and that they frequently use both mudflats and grasslands over the winter and spring (buffer effect paper). Colour-ring studies show that birds tend to use the same sites in the same seasons every year (as discussed in Generational Change). The study of tagged birds in France allowed researchers to add daily detail for a small number of Black-tailed Godwits.

The study was carried out on the French Atlantic coast, from the Loire Estuary area, in the north, through the Baie de Bourgneuf and the Vendée Coast, and south to the Pertuis Charentais area. Full details of available habitats are provided in the paper.

Follow those godwits

The tags on the study birds were set to provide locations every thirty minutes. The ten individuals that are the focus of the Jourdan paper provided a mean of 41 locations per day, rather more than can be obtained from colour-ring reading!

At a large spatial scale, the 10 monitored Black-tailed Godwits could be split into two groups:

Six godwits (BLTG11, 12, 14, 16, 17 and 18) remained within the Pertuis Charentais area throughout their tracked period, exploiting a small number of distinct sites. The average distance travelled in a day varied from 10 km to 31 km, depending on the individual, sometimes exceeding 40 km in one day. These birds were largely coastal, feeding on intertidal areas, but some of them occasionally visited inland habitats around the major roost sites.
Four godwits (BLTG13, 15, 19 and 20) spent the early and mid-winter period in Pertuis Charentais but then flew north, to the Loire-Bourgneuf area, either directly or with a stop at the Olonne Marshes on the Vendée Coast. These refuelling stations were also used during pre-migration and post-migration periods. BLTG13 and BLTG15 were monitored during two successive years and behaved consistently between years. BLTG19 was tagged as a juvenile and, as expected, stayed in France over the course of a full eighteen-month period.

*BLTG13 behaved consistently in two winters*

When it came to habitat use, the authors found it difficult to describe general patterns. This is important; mitigation measures aimed at providing alternative feeding areas tend to focus on the one-size-fits-all principle. In the detail presented in the paper, we see that different birds behave very differently. Wet grassland is not going to be a replacement habitat for a Black-tailed Godwit that specialises on feeding in tidal seagrass beds. Here are a few gems from the paper:

BLTG13 and 15 showed annual consistencies in their habitat selection but behaved very differently to each other. BLTG15 mainly used bare mudflats between August and February and selected inland marshes just before migration and upon return from Iceland. BLTG13 mainly used inland marshes in the run-up to departure (mid-February to mid-May) and upon return, using other habitats (saltpans, coastal marshes and mudflats) during the wintering period (early August to mid-February).
Individual birds switched habitat between three and eight times per month, often using multiple habitats during the course of a single day. Several birds spent long periods focusing on intertidal areas but then roosted on marshes or in saltpans, but even here there were exceptions. Having been part of the mud/marshes group, BLTG14 started prospecting inland to marshes and hunting ponds. This bird was one of two that used hunting ponds more intensively, both by day and by night, after the shooting season closed at the end of January.
Important habitats included inland marshes, hunting ponds and salt pans, with BLTG11 feeding almost exclusively in salt pans and ignoring tidal feeding opportunities. It was also clear that some birds were feeding at night more than had previously been thought.

*BLTG13 and BLTG15 illustrate the different mixes of habitats that are used by individual Black-tailed Godwits*

*One of the tagged birds, breeding in Iceland*

The movements at both local and large scales underlined the use of multiple habitat types, in both marine areas and freshwater wetlands. Most birds predominantly used intertidal areas from early to mid-winter and then moved to inland marshes just before the spring migration period, but they also showed an ability to shift quickly from natural habitats to artificial wetland habitats such as saltpans or hunting ponds.

Looking at the distribution of Black-tailed Godwits across a wide range of habitats, it may be tempting to think that this is a flexible species. Birds certainly seem able to identify new opportunities that become available as the season progresses, such as switching to grassland feeding when estuaries become less productive and then using hunting ponds once duck shooting is over. However, once a bird has adjusted to its own rhythms, it remains faithful to its own patterns of habitat use between years.

Conservation challenges

Many of the estuaries of Europe are protected from further development, at least to some extent, thanks to European legislation but rarely do the boundaries of Important Bird Areas extend beyond beaches and sea walls. As Clément Jourdan and his colleagues show, Black-tailed Godwits commonly use feeding areas that lie outside designated areas, especially during the period when they are fattening up for spring migration. As the authors point out, inland pools can also be important roost sites, as described in A place to roost, which highlights the Gilroy ‘godwit field’ near the Dee Estuary of northwest England. This small site can be used by 5% or more of the Icelandic population of Black-tailed Godwits during high spring tides in early autumn.

The boundaries of estuaries have been defined by the sea walls that protect towns, villages and agricultural land but this is an artificial system. Four centuries ago, waders could move freely between estuaries, brackish lagoons and freshwater marshes. These days, waders such as Black-tailed Godwits fly tens of kilometres to find the mix of habitats they need. Studies of these ten birds add rich detail to the picture painted by colour-ring sightings, as discussed in Godwits and Godwiteers.

The ‘near-threatened’ Curlew is even more of a challenge for conservationists. Curlew spend a lot of their time on estuaries but also use nearby fields and grasslands as roosting and feeding sites. Forth Estuary Curlew that can be seen on rugby pitches in Edinburgh are probably not going to be disturbed more than a few times a week but a new £150 million distribution centre at West Melton in Hull is permanently removing fields used by Humber Estuary birds.

We know that other wader species, such as Golden Plover and Oystercatcher flip backwards and forwards between marine and terrestrial feeding/roosting areas but tracking may well show that such behaviour is more widespread than we thought across species of wader.

Godwits in France

This paper provides fascinating insights into the lives of individual Black-tailed Godwits. There are too few tracked birds for formal analyses of habitat preferences but there are enough differences within the ten individuals to show that the removal of one site from a winter network can have wider implications than might have been expected. The full Wader Study paper is available here:

Combination of marine and freshwater artificial habitats provide wintering Black-tailed Godwits with landscape supplementation. Clément Jourdan, Jérôme Fort, Frédéric Robin, David Pinaud, Philippe Delaporte, Didier Desmots, Alain Gentric, Pamela Lagrange, Julien Gernigon, Loïc Jomat, Pierre Rousseau & Pierrick Bocher. Wader Study. DOI 10.18194/ws.00271

What happens when the mud disappears?

October 15, 2022October 17, 2022 / Graham Appleton / 3 Comments

The Yellow Sea provides important ‘service stations’ for shorebirds on the East Asian-Australasian Flyway, especially on their way north to Russian and Alaskan breeding areas. In a thought-provoking paper in Biological Conservation, Xiaodan Wang and colleagues consider how assemblages of waders have changed, as available habitat has been lost on this flyway. Their results suggest that conservation of these migratory shorebirds will depend upon lots of local initiatives.

The Yellow Sea

As discussed in Wader declines in the shrinking Yellow Sea, based on a paper by Colin Studds et al, the number of shorebirds on the East Asian-Australasian Flyway (EAAF) has fallen significantly. The rapid decline has been linked to a sudden drop in the survival rates of adults, especially in Bar-tailed Godwit, Red Knot and Great Knot. For these three species, the proportion of adults dying each year doubled over a period of just three years, with a strong link between species’ dependence upon the Yellow Sea and the rate of decline in numbers. This study and other papers have spawned welcome conservation initiatives and collaborative research programmes in China, South Korea and the Democratic People’s Republic of Korea.

In the most recent appraisal of numbers for EAAF shorebird species that travel as far as Australia, it is estimated that the number of Far Eastern Curlew has dropped to just 35,000 individuals and that there was a 50% drop in numbers for Curlew Sandpiper and Red Knot between assessments in 2008 and 2021. These catastrophic changes show how quickly things can go wrong, especially when adults struggle to get through the annual breed-migrate-moult-fatten-migrate cycle.

In their paper, Xiaodan Wang et al compared the results of shorebird surveys on the Yellow Sea coast of China during northwards migration, between an “early” study period (1996 to 2005) and a “late” study period (2013 to 2014), at 14 stop-over sites. These are sites where large areas of tidal habitat have been destroyed.

What happened?

In their study, the authors investigated three hypotheses:

Are trends in population numbers at stopover sites (in China) similar to those detected in nonbreeding sites (e.g. Australia)?
Is the diversity within shorebird communities linked to habitat condition?
How does a reduction in the area of tidal habitat affect numbers of waders and the composition of shorebird communities?

Counting shorebirds

China’s Yellow Sea region, which extends from the Yalu Estuary (Liaoning Province) in the north, to the Yangtze Estuary (Shanghai) in the south, holds the largest areas of intertidal mudflats in the world. The first comprehensive spring shorebird surveys along this Yellow Sea coast were conducted between 1996 and 2005 (the early period in this study). The Yellow Sea coast was surveyed again in 2013 and 2014 (the late period), by which time large areas of several intertidal flats had been ‘claimed’ and turned into farmland and industrial zones. See paper for methods.

A total of 14 sites were surveyed at similar times, in the early and late periods, enabling comparisons of community richness, the abundance levels of individual species and the density of birds across the available feeding habitat. The key results of the study are:

Counts: The measured decline in bird numbers was on a scale which was less dramatic than those reported from Australia. At the 14 stopover sites, a total of 668,995 individuals of 44 species were recorded in the early period, and a total of 617,146 individuals of 43 species were recorded in the late period. This corresponds to a 7.8% reduction between the early and the late periods.

Species richness: There was much variation between sites, with between 18 and 38 shorebird species recorded, but the numbers of species on each study site were similar between the two periods.

Distributions: Decreased abundance was recorded at ten sites and increased abundance was recorded at four sites. The number of birds on the Liaohe Estuary trebled between the early and late periods, mostly due to the discovery of a flock of 80,000 Great Knot. A recent population assessment of shorebirds of the East Asian-Australasian Flyway suggests that this large flock accounts for 20% of the world’s Great Knot. These passage flocks of Great Knot tend to stay for only a few days, making it hard to reliably pick up any changes between years.

Change across the region: No significant differences were found in species richness or abundance at the same sites, between the periods, but there were significant differences among sites. Ten species were recorded in smaller numbers, with increases for Bar-tailed Godwit (up 16.8%) and Great Knot (57%).

Communities: Bird assemblages at each site were similar in the two study periods, with the commonest species remaining the same. For example, Great Knot and Bar-tailed Godwit are the dominant species in the Yalu Estuary, while Red Knot and Curlew Sandpiper are the dominant species in North Bohai Bay, in both periods.

Loss of habitat: The total tidal flat area decreased by 35.6%, from 4017 km² in the early period to 2588 km² in the late period. Habitat loss was detected at all of the 14 sites. More than half of the tidal flat was destroyed at Northern Bohai Bay, Laizhou Bay, Southwest Bohai Bay, and Jinzhou. Relatively small losses (< 10%) occurred at Chongming Dongtan, Yalu Estuary, Jiaozhou Bay, and Liaohe Estuary (see map).

Shorebird densities: Shorebird densities (birds per km²of mudflat) differed markedly between sites. During the study period, the estimated bird density increased at 7 sites and decreased at 5 sites, with an overall increase in density of over 40% between the early (1996-2005) and late (2013-2014) periods.

Bit of a squeeze?

‘Land claim’ – turning mud flats into farmland and industrial areas – reduced the amount of available feeding habitat in the Yellow Sea study area by 35% between 1996-2005 and 2013-2014. If the same numbers of waders were to be accommodated, then that would imply increases in densities of about 55%. This assumes that feeding conditions remain the same and that spring fattening can happen just as quickly, despite the higher densities. If it’s harder to find food, birds will potentially need to stay longer, to fatten up for the next part of their migration, and that suggests that densities would need to be even higher. The observed change in density of 40% is lower than 55% but this may be consistent with falling populations.

What might be happening?

It is clear that wader numbers in the Yellow Sea have declined, as expected from annual counts in Australia and New Zealand. However, the decline in spring numbers is not as dramatic as might have been predicted. The remaining birds have much less space in which to feed and densities have increased, suggesting that there will be more competition for resources than there was a decade previously. Returning to the three hypotheses put forward by the authors:

Are trends in population numbers at stopover sites (in China) similar to those detected in nonbreeding sites?

Bird surveys covered the same zones and were conducted on similar dates in the early and late periods. Changes in shorebird counts during the study periods did not always exhibit the same population trends as those at nonbreeding sites in Australia and New Zealand.

Is the diversity within shorebird communities linked to habitat condition?

The fact that there are different mixes of waders on different estuaries is probably linked to different food resources. It would be good to know more about the food that is available to species as diverse as small sandpipers and large curlew – especially in the earlier period before so much habitat was lost. Red Knot and Great Knot give hints that waders are found on sites that are appropriate to their needs, with more Great Knot on Yalu Estuary, where the key shellfish they eat (Potamocorbula laevis) are larger, and more Red Knot at Nanpu, where the shellfish are smaller. Given the expected links to available feeding opportunities on individual sites, it is unsurprising that the diversity of shorebird communities has tended to remain the same.

How strong is the link between the change in the area of tidal habitat lost and the changes in the numbers of waders and the composition of shorebird communities?

The research team expected to find changes in shorebird numbers and species composition but the relationships are not as strong as might have been expected, given the areas of mudflat that have been lost.

There is no clear pattern of community change, as just discussed, and this is in line with analyses of more comprehensive annual Wetland Bird Survey data, collected in the United Kingdom. As population levels fell, the changes were spread across all estuaries. Some people may have predicted that distributions would have become more focused on ‘better’ estuaries but this was not the case for wintering waders. Ringing studies suggest that individuals’ site-fidelity is strong, which reduces the potential for distributional change. This study is described in the WaderTales blog, Interpreting changing wader counts, which summarises a paper in Diversity & Distributions, by Méndez et al.

In the Studds paper, there is a clear signal that species that are more dependent on the Yellow Sea exhibited the steepest declines in numbers, so it seems unlikely that there was an excess of available food at the time of the first surveys (1996-2005). If food supplies are limiting, why is the link between habitat lost and numbers not stronger?

*The latest estimate of the flyway’s Far Eastern Curlew population is just 35,000*

Xiaodan Wang et al discuss why they did not see a clearer relationship between mudflat loss and changes in shorebird numbers. They suggest that population declines may be less severe in some (or even all) of the study sites than might have been expected because these are known hot-spots for waders. Losses may have been more dramatic elsewhere. We know that severe habitat loss can remove most waders from a site, leading to redistribution of affected birds.

It is also possible that individual birds could be staying longer at spring staging sites in the Yellow Sea, due to poorer feeding conditions or changes to the timing of migration. This build-up of birds could mask the scale of the real declines in numbers using Yellow Sea mudflats. In the future, information gleaned from tracking and through resightings of colour-ringed birds should help to monitor stop-over times. Sadly, similar data are not available for the period 1996 to 2005.

Conservation Implications

This paper provides another reminder that structured surveys are immensely valuable. Back in 1996, could anyone have imagined how quickly China’s Yellow Sea mudflats would be turned into farmland and industrial complexes? Extending surveys to more estuaries in the East Asian-Australasian Flyway, using standardized protocols and sharing datasets, will be important, when assessing responses to habitat changes at breeding, stopover, and nonbreeding sites.

Studies at the species level, especially those focused on habitat specialists, have found that some birds cannot successfully relocate to alternate sites if their major staging sites are lost (e.g., Moores et al. 2016). This paper, by Xiaodan Wang et al, concludes that maintaining populations of migratory species along the East Asian-Australasian flyway depends upon the conservation of an extensive network of estuaries within the Yellow Sea.

Paper

The full paper can be accessed here:

Impacts of habitat loss on migratory shorebird populations and communities at stopover sites in the Yellow Sea. Xiaodan Wang, Ying Chen, David S.Melville, Chi-Yeung Choi, Kun Tan, Jiajia Liu, Jing Li, Shoudong Zhang, Lei Cao & Zhijun Ma. Biological Conservation.

UK waders: “Into the Red”

October 4, 2022October 11, 2022 / Graham Appleton / 4 Comments

If you ask British birdwatchers to name the eleven wader species that are causing the most conservation concern in the UK, they would probably not include Dunlin. Curlew may well be top of their lists, even though the most recent population estimate is 58,500 breeding pairs, but would people remember to include Ruff?

This blog is a new incarnation of Nine Red-listed UK Waders, explaining why there are now eleven shorebird species on the UK Red List. Its publication coincides with the appearance of the BTO book Into the Red which highlights the problems being faced by seventy species that breed and/or spend the winter in the United Kingdom. The work of seventy writers and seventy artists has been curated by Kit Jewitt (@YOLOBirder on Twitter) and Mike Toms (BTO), and the book is being sold to support the work of both the BTO and the Rare Breeding Birds Panel.

What’s a Red List?

The UK Red List is made up of a strange mixture of common and rare species. Nobody will be surprised to see fast-disappearing Turtle Dove and Willow Tit, but why are 5.3 million pairs of House Sparrow (right) in the same company?

The list is very important because it helps to set the agenda for conservation action, influences the way that money for research is distributed and focuses attention during planning decisions. The main criteria for inclusion are population size – hence the inclusion of species that are just hanging on in the UK, such as Turtle Dove – and the speed of decline of common species. Data collected by volunteers, working under the auspices of the British Trust for Ornithology (BTO), measured a population decline for House Sparrow of 69% between 1977 and 2018, which is worrying enough to earn this third most numerous breeding species in the UK a place in Into the Red.

Mark Eaton of the Rare Breeding Birds Panel explains how listing works.

The Birds of Conservation Concern (BOCC) system, through which the Red List and Amber Lists are determined, uses a strict set of quantitative criteria to examine the status of all of the UK’s ‘regularly’ occurring species (scarce migrants and vagrants aren’t considered), and uses a simple traffic light system to classify them. There are ‘Red’ criteria with thresholds for rates of decline in numbers and range, historical decline and international threat (if a species is considered globally threatened it is automatically Red-listed in the UK), together with a range of other considerations such as rarity, the international importance of UK populations, and how localised a species is. If a species meets any of the Red List criteria it goes onto the Red List.

This blog is about the eleven waders in Into the Red, but there are 59 other fascinating species accounts and wonderful artworks. Each of the species accounts below starts with a quote from the book and is accompanied by a low-resolution version of the artwork.

Dotterel

“Dot, dot, dot, Dotterel. Disappearing – a dash, dashing off the page.” – Alicia Hayden

The UK’s small population of Dotterel is restricted to the high tops of Scottish mountains, with only occasional breeding reports elsewhere. Three decades ago, the warning bells were raised, as warming conditions and an elevated snowline turned the Dotterel into a poster bird for climate change campaigners. The detailed reasons for the species’ decline may still need to be nailed down but candidate causes, such as declining insect food supplies and the increasing numbers of generalist predators, are probably all linked to a changing climate – squeezing Dotterel into a smaller area of the mountain plateaux of Scotland.

There’s a blog about the decline in Dotterel numbers called UK Dotterel numbers have fallen by 57%, based upon a paper that uses data up until 2011. At this point, the population was estimated at between 280 and 645 pairs. There has been no suggestion of improvement since that blog was written. Interestingly, Dotterel may have a way out of their predicament, as we know that marked individuals move between Scotland and Norway in the same breeding season. See also Scotland’s Dotterel: still hanging on, which highlights the pressures that youngsters face in North Africa, during the first eighteen months of their lives.

Ringed Plover

“The gentle scuttle over the rocks, the unmistakable bum-bob and the elegant glide into a nest site” – Dan Rouse

One of the criteria that the BOCC panel takes into account, when constructing the Red List, is the responsibility the UK has for a species or subspecies in the breeding season, during winter or both. The Ringed Plovers we see in the UK in the winter are almost exclusively of the hiaticula subspecies; birds that breed in southern Scandinavia, around the Baltic, in western Europe and in the UK. There are only estimated to be 73,000 individuals in this subspecies, so the 42,500 that winter in the UK constitute a large percentage of the Ringed Plovers that breed in many of these countries.

The Wetland Bird Survey graph shows a decline of over 50% between 1989 and 2014. At the start of the period, Ringed Plover numbers were at an all-time high but this is still a dramatic and consistent drop. Numbers on the open coast did not drop as much (see Waders on the coast) and those on estuaries may have stabilised or even have increased slightly, since 2014, but Ringed Plovers need some good breeding years. Disturbance is an issue for nesting Ringed Plovers, which share their beaches with visitors and dogs, as discussed in this blog about the ‘no go’ areas along the Norfolk and Suffolk coasts – On the beach. Winter disturbance can be a problem for waders too (see Disturbed Turnstones).

Lapwing

“I heard them before I saw them. Like the plaintive squeak of a rubber toy, or an oboist tuning up …” – Tessa Boase

The Lapwing used to nest across the whole of the United Kingdom and was a common bird in almost every village. It’s still the most numerous breeding wader in the UK, with 97,500 pairs (APEP4), beating Oystercatcher by just 2,000 pairs. Numbers dropped by 55% between 1967 and 2018, according to BirdTrends 2020, published by BTO & JNCC. Huge losses had already occurred over the previous two centuries, as land was drained and vast numbers of eggs were collected for the table. The Lapwing is now a bird associated with lowland wet grasslands and the uplands, rather than general farmland.

Red-listing has been important for Lapwing, increasing the profile of the species and encouraging the development of specific agri-environment schemes targeted at species recovery. These include ‘Lapwing plots’ in arable fields and funding to raise the summer water tables in lowland grassland. Several WaderTales blogs describe efforts to try to increase the number of breeding waders in wet grassland, especially Toolkit for Wader Conservation. The loss of waders, and Lapwings in particular, from general farmland is exemplified in 25 years of wader declines. There are many predators that line up to take Lapwing eggs so it pays to nest in loose ‘colonies’, so that guard duties can be shared.

Whimbrel

“Whimbrel have been doing this journey, between tundra and heath of northern Europe to mudflats and mangroves of Africa, for at least 1.9 million years” – Rosie Ellis

Most British and Irish birdwatchers think of Whimbrel as spring migrants, enjoying seeing flocks of Icelandic birds when they pause on their way north from West Africa (see Iceland to Africa non-stop). There is a small, vulnerable UK population nesting almost exclusively on Shetland. The latest estimate is 290 pairs (2009), down from an estimate of 530 pairs, published in 1997. We await the results of a 2021 survey with interest. Many pairs have been lost from Unst and Fetlar and this blog about habitat requirements might give clues as to why: Establishing breeding requirements of Whimbrel.

The curlew family is in trouble across the Globe, potentially because these big birds need so much space (see Why are we losing our large waders?). Hints of future issues for Eurasian Whimbrel are coming from Iceland, where forestry is squeezing them out of some key areas: Iceland’s waders need a strategic forestry plan.

Curlew

“A song that seems to split in mid-air and take the heart in two directions at once” – David Gray

What more can be said about Curlew, ‘promoted’ to the red list in 2015 and designated as ‘near threatened’ globally. Most significant is the story from Ireland, where 94% of breeding birds disappeared in just 30 years. These blogs provide more information about the decline and review some of the reasons.

Across every part of the UK, stakeholder groups have come together to support populations of breeding Curlew, using a mixture of habitat management, predator reduction and nest protection measures. One recent innovation is to raise chicks in captivity, in an attempt to boost local populations in England. There’s more in Will head-starting work for Curlew?

Black-tailed Godwit

“These birds become old friends and open our eyes to the world of migration” – Jennifer Gill

Winter Black-tailed Godwit numbers are booming but these are islandica – birds that have benefited from warmer spring and summer conditions in Iceland, as you can read here in: From local warming to range expansion. Their limosa cousins are in trouble in their Dutch heartlands (with declines of 75%) and there have been similar pressures on the tiny remaining breeding populations in the Ouse and Nene Washes, as you can discover in England’s Black-tailed Godwits. A head-starting project in the Washes is boosting the number of chicks; so much so that released birds now make up more than a quarter of this fragile population. Red-listing has shone a spotlight on this threatened subspecies, attracting the funding needed for intensive conservation action.

Ruff

“But then, good grief, in May and June, I’m treated to a different plume; A glorious crown, I gush and swoon – and then, no doubt, I change my tune.” – Jess French

Some Ruff spend the winter months in the UK and numbers are boosted in spring as birds pass through on their way from Africa to Scandinavia and the Baltic countries. Occasionally, males in glorious breeding attire will display in leks, perhaps attracting the attention of females. As a (very) scarce breeder, Ruff automatically earns a place on the Red List.

250 years ago, Ruff were breeding between Northumberland and Essex, before our ancestors learnt how to drain wetlands and define a hard border between the North Sea and farmland. Hat-makers, taxidermists and egg-collectors added to the species’ woes and, by 1900, breeding had ceased. The 1960s saw a recolonisation and breeding Ruff are still hanging on. Lekking males cause excitement in sites as disparate as Lancashire, Cambridgeshire and Orkney, and there are occasional nesting attempts. Habitat developments designed to help other wader species may support Ruff but the situation in The Netherlands does not suggest much of a future. Here, a once-common breeding species has declined to an estimated population of 15 to 30 pairs (Meadow birds in The Netherlands).

Dunlin

“Memories of sunny days, swirling flocks of waders and blisters from closing metal rings still linger. How can a bird that was so numerous less than 50 years ago now be Red-listed?” – Graham Appleton

There are good reasons for the addition of Dunlin to the UK Red List; breeding numbers of the schinzii race have declined significantly and the number of wintering alpina Dunlin in Great Britain dropped 10,000 between two periods that were only eight years apart, as you can read in this blog about population estimates for waders.

The fall in breeding numbers is probably the bigger problem, as indicated by range reductions in successive breeding atlas periods (1968-72, 1988-91 and 2008-11). It’s hard to monitor what is happening to numbers on a year-by-year basis because the breeding distribution is too patchy and thin to be picked up via the Breeding Bird Survey. Alarm bells are being raised in Ireland, where numbers have dropped to between 20 and 50 pairs (Status of Rare Breeding Birds across the island of Ireland, 2013-2018), and in the Baltic, where numbers have fallen by 80% since the 1980s. There’s a WaderTales blog about Finnish Dunlin.

The winter decline in the UK may or not be an issue, although it has to be considered as part of large-scale moderate losses across the whole of western Europe. There is a theory that, over the years, as winter conditions on the continental side of the North Sea have become less harsh, new generations of juvenile alpina have settled in countries such as the Netherlands, instead of continuing their southwesterly migrations from northern Russia. Once a wintering site has been chosen, individuals are site faithful, so one ends up with newer generations on the continent and ageing adults in the UK and Ireland. WeBS counts for Dunlin are half what they were 25 years ago.

Purple Sandpiper

“It’s an easy species to overlook, the Purple Sandpiper. For a start, they’re not purple” – Mark Eaton

Purple Sandpiper earns its red listing because a very small number of pairs nest in Scotland. Proof of successful breeding is rare and the species may drop off the list at the next review, as Temminck’s Stint did in 2015. Extirpated species (birds that no longer breed) are not red-listed.

In winter, the rocky coasts of the UK are home to Purple Sandpipers from the Arctic, with a suggestion that North Sea coasts, south of Aberdeen, mainly play host to birds from Spitsbergen and northern Scandinavia, with Greenlandic and Canadian birds more likely to be found further north and on the Atlantic coast. Coastal numbers declined by 19% between 1997/98 and 2015/16, according to the Non-estuarine Waterbird Survey, and WeBS counts suggest numbers have at least halved over a period of 25 years. The Highland Ringing Group has shown that the number of young Purple Sandpipers has been declining on the Moray Firth, suggesting several years with relatively poor breeding success, for birds migrating from the northwest, or short-stopping by new generations of youngsters, as discussed for Dunlin. Perhaps they are wintering in Iceland these days?

Woodcock

“Like clockwork, I’d encounter this sight at 7 pm each summer evening as one flew over my head in the back garden, heading towards the thick woodland.” – Megan McCubbin

The presence of Woodcock on the Red List causes heated debate; how can this still be a game species? Red-listing is indisputable; the most recent survey by BTO & GWCT showed that there was a decline in roding males from 78,000 in 2003 to 55,000 in 2013, with the species being lost from yet more areas of the UK. Each autumn, the number of Woodcock in the UK rises massively, with an influx of up to 1.4 million birds. Annual numbers depend upon seasonal productivity and conditions on the other side of the North Sea. A recent report on breeding wader numbers in Norway, Sweden and Finland, shows that breeding populations of Woodcock in this area are not declining (Fennoscandian wader factory).

The UK’s breeding Woodcock population is under severe threat from things such as increased deer browsing and drier ground conditions but winter numbers appear to be stable. The difference in conservation status between breeding and wintering populations is reflected in the fact that Woodcock is on both the Red List and the Quarry List, for now. There is a WaderTales blog (Conserving British-breeding Woodcock) that discusses ways to minimizes hunting effects on British birds. These guidelines from GWCT emphasise the importance of reducing pressures on British birds.

Red-necked Phalarope

“The evening light was beautiful, and it was just amazing to watch it spinning around in characteristic fashion” – Dawn Balmer

Red-necked Phalaropes that breed in Shetland and a few other parts of northern Scotland appear to be an overflow from the Icelandic population; birds which migrate southwest to North America and on to the Pacific coastal waters of South America. This BOU blog describes the first track revealed using a geolocator.

The Red-necked Phalarope was never a common breeder and came under pressure from egg-collectors in the 19th Century. Numbers are thought to have recovered to reach about 100 pairs in Britain & Ireland by 1920. Numbers then fell to about 20 pairs by 1990, so the latest estimate of 108 pairs in 2018 reflects conservation success (The Rare Breeding Birds Panel). Given the restricted breeding range and historical declines, it is unlikely that the next review will change the conservation status from Red to Amber, despite the recovery of numbers.

In conclusion

The Red List creates some strange bedfellows. In the book, Turtle Dove follows Herring Gull (right); a bird with links to love and romance and another with at best the charm of a roguish pirate. But the List works; it creates an evidence-base that help those who devise agricultural subsidy systems, advise on planning applications, license bird control and prioritise conservation initiatives.

Into the Red aims to raise awareness of the UK’s most at-risk bird species, eleven of which are waders, and to raise money to support the Rare Breeding Birds Panel and BTO research scientists. This is a follow-up to Red67, published in 2019 and based on the Red List from 2015. It is sad that this version covers 70 species, rather than 67. Worryingly, the first Red List, produced in 1990, only had 36 species on it.

Into the Red is a lovely book that captures the thoughts and images of a generation. Details of how you can order a copy from the BTO can be found here.

A Whimbrel’s year

September 22, 2022May 14, 2023 / Graham Appleton / 4 Comments

There’s a lot to fit into twelve months if you’re a Whimbrel. In the last paper from his PhD, Camilo Carneiro assesses whether Icelandic Whimbrel can always manage to complete the annual cycle of migrate-breed-fatten-migrate-moult-fatten in just 365 days.

*YY-LL (Yellow yellow – lime lime) collected data for several years.*

What happens if a pair of Whimbrel loses a first clutch and a successful, late breeding attempt delays departure from Iceland, for instance? Is there the flexibility to make up for lost time during a west-African winter? Some answers are provided in a paper by Camilo Carneiro et al in The American Naturalist.

Facing the consequences

We know that large waders sometimes take a year off from breeding, as discussed in Teenage waders, suggesting that they may not always have the resources they need to breed every year. This blog, based on a paper by the Bird Ecology Lab team in Chile, tells the tale of a few Hudsonian Godwits that headed for the pampa grasslands of Argentina in spring, instead of migrating to Alaska.

As discussed in Gap years for sandpipers, taking a year off may make no difference to expected lifetime breeding output and could be more common when individuals spend the non-breeding season a long way from nesting areas or in poor quality sites. If Iceland’s Whimbrel are able to compensate for any delays they face during the course of the annual cycle then perhaps that suggests that all is well for this population that migrates all the way to West Africa at the end of the summer breeding season?

The story so far

Whimbrel only spend three months of the year in Iceland, with the rest of the time spent some 6000 km further south. In July or August, an adult will exchange the sparsely vegetated river plains and night-time frosts of Iceland for mud, mangroves and tropical temperatures. The diet changes too, from terrestrial invertebrates and crowberry to crabs.

Camilo Carneiro started a PhD on Iceland’s breeding Whimbrel in 2015, continuing the work of his supervisors, Tómas Gunnarsson of the University of Iceland and José Alves from the University of Aveiro (Portugal). Using geolocator tags he investigated the capacity for Whimbrels to undertake non-stop journeys, demonstrating that autumn migration was generally direct but spring migration for most birds included a stop, often in Ireland or the UK. You can read more in Iceland to Africa, non-stop. Birds that need to (or choose to) take a break delay their arrival in Iceland by about ten days.

Subsequent papers by the same team have shown that the most consistent point of the annual migration story is departure from Africa and shown links between weather and phenology. These two papers have been covered in the WaderTales blogs Whimbrel: time to leave and A Rhapsody of Whimbrel. In an attempt to discover the best places to spend the winter months, Camilo analysed tag and colour-ring data to work out links between conditions experienced in wintering locations and subsequent breeding success, as discussed in the blog Winter conditions for Whimbrel.

Seven years of data

To investigate how migratory animals navigate their annual schedule, and where and when they can make adjustments to their timings, Camilo Carneiro and his colleagues used annual-cycle data of 38 Icelandic whimbrels tracked over 7 years. They asked three questions:

Does the change in the timing of one event in the annual calendar, such as a late breeding season, affect the timing of subsequent events, perhaps with further down-stream domino effects?
Can individuals compensate for delays, on migration for instance, by spending less time on the next stage of the annual cycle, e.g. by reducing a stop-over?
Are there potential fitness consequences? Do birds that are subject to delays breed later? In waders, earlier chicks are more likely to recruit to the breeding population so being just a few days late returning to Iceland may have consequences.

During the period 2012 to 2018, a total of 78 geolocators were deployed on Whimbrel breeding in Southern Iceland. The device was attached to a leg-flag in one year (see picture) and usually collected in the subsequent breeding season. In most cases, a replacement geolocator was fitted, in order to collect further data on that individual. Unsurprisingly, it became harder to catch tagged birds over time, as birds learned to recognise nest traps and research vehicles. The fact that so much valuable information was collected from the same birds is testament to Camilo’s patience. Sixty-six geolocators were retrieved from 39 individuals. Birds could only be caught when incubating a full clutch of eggs so nest losses due to predation affected the likelihood of recapture.

Please see the paper in The American Naturalist for full details of the methods used to collect data on breeding success and for interpretation of data collected using geolocators.

Whimbrel YY-LL

Before looking at the results in the paper, here’s an example of data collected using geolocators, for two years in the life of YY-LL (Yellow Yellow – Lime Lime), pictured alongside.

In 2015, YY-LL nested successfully and left Iceland on 16^th August. After four days of direct flight, he reached Guinea-Conakry. His nesting attempt in 2017 was unsuccessful and he migrated south a little earlier, on 5^th August, again taking four days to fly 6000 km.

In the springs of both 2016 and 2018, YY-LL left the winter grounds on 22^nd April, arriving in Ireland on 26^th April in 2016 and on 25^th April in 2018. Migration from Ireland to Iceland took place between 5^th and 7^th May in 2016 and between 7^th May and 9^th May in 2018.

YY-LL hints at strong consistency of spring migration timing, independent of nest success.

Results

The 38 tagged Whimbrel provided information about 76 autumn migrations and 60 spring migrations. Most of the birds (89%) spent the winter between Senegal and Sierra Leone, particularly in Guinea-Bissau and Guinea, with one bird in Portugal and the rest in coastal northwest Africa.

As is usual in waders, females left Iceland before males, the difference being typically around six days. Although failed breeders did depart earlier than birds that successfully reared chicks, the difference was not great, again averaging around six days.

There was no suggestion that birds that left Iceland late in the season ended up on a delayed schedule for return to Iceland in the subsequent spring. This implies that resources in Africa were sufficient to ‘catch up’ with earlier birds, despite the need to complete a full moult and to prepare for another 6000 km migration.

As indicated in previous papers (and in the blogs mentioned above) spring departure dates of tagged birds from Africa were not different for different countries or for different sexes. However, birds that stopped in Europe tended to leave Africa earlier (19^th April on average) than those that made direct spring flights (30^th April). These latter birds tended to arrive in Iceland about a week earlier than birds on a two-stage migration, representing a neat, overtake manoeuvre! Typically, males arrived in Iceland about a week earlier than females.

For the sample of tagged birds, neither the autumn departure date from Iceland nor wintering location had any apparent effect on the arrival date in the next spring.

There seems to be a strong signal that, just as YY-LL did, an individual Whimbrel can make up for any delays incurred, with birds that arrive at a location later spending less time there, whether that be a wintering site or a spring stopover location. Females tended to spend longer at spring stopover locations, which ties in with the earlier arrival of males in Iceland. The graph alongside illustrates these two points. Birds that left Africa earliest spent more than 15 days at stopover sites but birds on a later schedule stopped off for as few as 6 days. Triangles represent males and squares are females.

Over the course of a year

Putting this all together, Camilo and his colleagues found that individuals appear to use the wintering sites to compensate for delays, these mostly having been associated with a successful previous breeding season. The wintering season is up to 38 weeks long so a Whimbrel that heads south a little late has plenty of time in which to catch up with earlier birds. The timings for other wader populations that spend shorter periods in wintering locations may be more constrained, given that post-breeding moult might take 20 weeks and the time to fatten up for migration can add an extra seven weeks.

Once a bird leaves Africa, it is harder to compensate for delays, although attempts are made to do so, with later individuals stopping for shorter times at spring stop-over sites and then nesting shortly after arrival in Iceland. Data in the paper suggest that it is not possible to catch up completely, before the start of the breeding season, if time is lost on the way north. Given the known link between lay-date and nesting success, these spring delays may have consequences for productivity and reduce the capacity to re-nest following clutch loss.

Iceland’s Whimbrel

Camilo’s research suggests that adult Whimbrel in the south of Iceland have the capacity to make up for any delays that they face during the annual cycle. The same may not be true for other large waders, the populations of which are mostly in decline. The blog Why are we losing out large waders? reminds us that two curlew species are thought to be extinct or on the verge of extinction and that most of the rest are in trouble.

*There are increasing pressures on Whimbrel breeding in Southern Iceland, associated with new forestry plantations and infrastructures such as road developments and power lines*

All is not necessarily well for Iceland’s waders either. Two 2022 papers by Aldís Erna Pálsdottir, looking at the effects of forestry and power-lines, suggest that the Whimbrel is one of the wader species most seriously impacted by ongoing changes to the Icelandic landscape, as discussed in Power-lines and breeding waders and Iceland’s waders need a strategic forestry plan. These pressures seem to be reflected in poorer breeding output, as suggested by counts of family parties of Whimbrel made by Tómas Gunnarsson and colleagues in annual June and July surveys.

Camilo’s paper may indicate that adult Whimbrel can cope with all that life throws at them but if they cannot raise enough chicks the species will still be in trouble. With financial support from the Icelandic Centre for Research, Camilo is now studying the challenges that chicks face, as they prepare for their first migration from Iceland to Africa.

Here’s the link to the paper:

Annual schedule adjustment by a long-distance migratory bird. Camilo Carneiro, Tómas G. Gunnarsson & José A. Alves. The American Naturalist. doi.org/10.1086/722566

Will head-starting work for Curlew?

August 31, 2022December 11, 2022 / Graham Appleton / 12 Comments

83 captive-reared Curlew were released successfully in 2019, over 130 in 2021 and a similar number in 2022 but this does not mean that head-starting is a solution to England’s Curlew problems. We don’t yet know the proportion of youngsters that survive the difficult ‘teenage years’, how many will find suitable breeding habitat and whether these birds can reliably raise chicks of their own. What have birds such as 7K, pictured here, revealed and what might happen next?

Exciting news

There has been some great TV and press coverage of head-started Curlew this summer (2022), with films of captive-reared birds being released from pens and flying for the first time. But what does the future hold for naïve birds that take to the air in Shropshire & Powys, the Severn & Avon Valleys of western England, Cornwall, Sussex and Norfolk? The first signs are good, as illustrated below in maps published by the BTO for the birds that they are tracking in Norfolk.

Satellite-tagged birds released at Ken Hill (Black stars – close to the Norfolk coast) can be seen flipping backwards and forwards between the mudflats and their release site, before beginning to explore more of the Wash estuary.

Birds released further inland, on The Sandringham Estate (White stars), started foraging in grassland areas and it took a while until any of these birds discover the coast. One bird “7Y” moved onto a little-used airfield (below), where it was seen with a flock of adults. It appears to have adopted a mudflat/grassland tidal routine, involving ‘commutes’ of ten miles each way, possibly having been guided by the adults (top row, third from the left).

*One of the Sandingrham youngsters joined up with a flock of adults on an airfield five miles from the release site*

It is easy to get ‘wowed’ by the TV reports and the individual stories of tracked birds but these are early days for Curlew head-starting. There’s a lot still to learn!

Why head-start Curlew chicks?

The Eurasian Curlew is in trouble, as you can read in the WaderTales blog “Is the Curlew really near-threatened?”. Annual survival rates of adults are high but productivity is low, with an estimate of 10,000 too few youngsters being fledged each year, to maintain population levels in the UK. The Irish Curlew population has crashed, providing dire warnings of what may happen soon in Wales, where there has been a decline of 73% since 1995 (Breeding Bird Survey). In southern England, most of the losses happened before 1995 and only a few populations remain, hanging on in areas such as Breckland in East Anglia.

Lessons from Black-tailed Godwits

We know that head-starting works well for limosa Black-tailed Godwits breeding in East Anglia but there was no guarantee that this would be the case when the WaderTales blog Special Black-tailed Godwits was published in 2017, to coincide with the departure of captive-reared birds from their WWT Welney release site. When the first birds not only returned in 2018 but actually raised their first chicks (see Head-starting Success), the approach looked to be successful. Over the following years, with more releases, the godwit population in the Ouse and Nene Washes has increased significantly. This temporary relief package for a beleaguered population has worked well, providing time to try to improve breeding conditions in the wild, so that Black-tailed Godwits can look after themselves. Head-starting is an intervention of last resort and cannot be a long-term solution to the problems faced by the species.

It is possible to support local populations of scarce birds, such as Bitterns and Little Terns, with interventions such as increasing areas of suitable habitat and protecting nest sites, but doing the same for Curlew will be more of a problem. Here, the challenge is to halt a decline of a species that breeds across wide areas of the UK, mostly on farmed land that is not being managed for conservation. Intensive, local action is not going to be enough. This is going to need teamwork between landowners, conservation organisations and volunteers – acting at a scale that has not been tried previously. Perhaps head-starting will help?

A pragmatic plan

The most recent UK population assessment of Curlew, in British Birds, suggested that there were 58,500 breeding pairs in 2016. Numbers have almost certainly dropped since then but the species is nowhere near as threatened as England’s breeding Black-tailed Godwits. The biggest Curlew head-starting programme, led and funded by Natural England, was a response to an opportunity to use unwanted Curlew eggs – not a ‘last-chance’ solution, as it had been for Black-tailed Godwits. Each year, Curlew eggs were being collected on RAF airfields, under licence, to deter adults and reduce airstrike risk. Thanks in no small part to Natural England’s Graham Irving, many of these eggs are now being head-started, instead of destroyed.

What happens to head-started birds?

The Natural England project builds upon the experiences of the Curlew Country team, working in the Shropshire hills and Powys borders. They released 6 head-started Curlew in 2017, 21 in 2018, 33 in 2019 and 34 in 2021. Raising extra chicks is part of an initiative that involves a broad range of stakeholders. See their website for more information.

The first stage of the head-starting process works well. Aviculturalists can rear and release chicks, with very high rates of success. They are learning more and more about the best diets, appropriate husbandry and the release process. Individual chicks wear small colour-rings, so that progress can be monitored daily, and they receive leg-flags and get weighed and measured before release. For instance, the young Curlew 7K featured above is a GPS tagged male that weighed in at a respectable 550 grammes when it was transferred to its release site on The Sandringham Estate, on 14 July 2022. By the end of August, it had moved to the Wash Estuary, as you can see in the figure above (top left map). There was a December report of 7K from a piece of amenity land on the edge of a new housing development in Hunstanton.

*Before transfer to The Sandringham Estate release site, a young Curlew is checked over by a vet*

From the start, the Natural England project has been built on partnerships. In the first year (2019), eggs were hatched and chicks were reared at WWT Slimbridge. Fifty young Curlew were released near-by and the first of these birds (wearing ring number 23) was found nesting near Gloucester in 2021, raising one chick of his own. In 2022, three years after release, five of the head-started Curlew were on breeding sites in the Severn and Avon area and one bird had moved to the Thames Vale. Male “23” shows that head-starting can add more Curlews to the breeding population but is he exceptional? What proportion of released birds make it this far and go on to raise chicks? The video by Kane Brides in this WWT blog tells the West Country story so far.

After a Covid-caused hiatus in 2020, the head-starting project expanded in 2021, with birds reared at both WWT Slimbridge in Gloucestershire and Pensthorpe in Norfolk. Richard Saunders, the Senior Ornithologist for Natural England, recognised the importance of learning what happens to newly-released fledglings and of monitoring potential recruitment. Working with Sam Franks of BTO and with lots of support from others, the Pensthorpe-reared Curlews are starting to reveal some of their secrets.

Where will the Pensthorpe birds set up home?

Most waders are philopatric; when they look for breeding sites, they tend to return to places close to the places in which they were raised. The release sites in North Norfolk were chosen not only because they provided suitable conditions for growing teenage waders, with low predator numbers and adults feeding nearby, but also because they are relatively close to current breeding sites, such as Roydon Common and the heaths of Breckland (see Curlews and foxes in East Anglia). There are also airfields, of course, and it will be unfortunate if birds choose these sites, given that eggs were removed to try to reduce bird-strike risk.

*Radio tag (left) will drop off when juvenile feathers are replaced. Satellite tag is mounted on a temporary harness and worn like a rucsac*.

All of the chicks are colour-ringed, some of them are radio-tagged and others are GPS-tagged, prior to release. By following tagged birds, as they explore the area around the release sites, the project aims to understand more about habitat use and to see if these naïve birds seem unduly prone to predation, given that they have not been trained to look out for danger by watchful parents. GPS tagging helps to paint the bigger picture; would birds move to the mudflats of the Wash and spend the whole winter in Norfolk or would some move on, to southern England, Ireland or France, for instance? These data will hopefully be augmented by reports of colour-ringed birds that do not carry tags.

*2C takes to the air after release at Ken Hill*

The first results have been encouraging. For example, a GPS tagged female from the first cohort released in Norfolk in 2021, wearing flag 0E, has followed the ‘stay local’ option. She spent the winter on the saltmarshes of RSPB Frampton, on the Wash in Lincolnshire, and has largely stayed on the south shore of the Wash through her first summer, showing no evidence of visiting any type of breeding habitat yet. A male Curlew wearing flag 4P has been more adventurous, spending the winter on the Exe Estuary in Devon, a site used by some adult Curlews that breed in Eastern England.

The amazing left-hand map below shows the route taken by ‘6Y’, one of the first batch of 2022 birds to be released on The Sandringham Estate. The story of this bird is told by the BTO’s Dr Sam Franks:

“The first of this year’s birds to migrate away from Norfolk departed at sunset last Wednesday & arrived on a Staffordshire field at sunrise on Thursday. It then flew towards Ireland & made an anxiety-inducing trip out into the Atlantic before returning to dry land.”

The right-hand map shows an overnight flight by ‘9L’, one of the last birds to be released from Ken Hill. This bird, pictured to the right , set off on the evening of 16th September, flew southwest overnight and headed south when it ran out of land. It landed in France at 01.30 on 17th. Although there is supposed to be a Curlew hunting ban in France (see this blog), three satellite-tagged birds from elsewhere in Europe were shot in the first weekend of the 2022 autumn hunting season. Will 9L survive the winter?

Data generated by colour-ring sightings will be analysed to check whether annual survival of youngsters in their first couple of years are consistent with figures for wild-reared chicks. This follow-up work is really important – the head-starting operation may seem to be successful but if few chicks survive long enough to breed then alternative approaches may be needed. Sightings of colour-ringed birds provide important information to add to data collected from tagged birds, which means that there is a vital role to be played by birdwatchers.

Around England

People care deeply about Curlew, as Mary Colwell explored in a recent book, reviewed in the WaderTales blog Curlew Moon, so it is not surprising that landowners feel inspired to help the species, by releasing birds on their own land. An attempt is being made to boost a tiny population on Duchy of Cornwall land on Dartmoor, using eggs from East Anglian airfields that were hatched at Slimbridge, and a licence has been granted to take eggs from a site in Northern England to be reared in Sussex, on an estate that appears suitable but where Curlew do not currently breed.

Release sites for these translocated birds do not hold many (or even any) Curlew so it will be interesting to learn whether the behaviour patterns of these fledglings are different to those of birds released in Norfolk and in the Severn and Avon Valleys of western England. All birds are being ringed, by WWT, GWCT and BTO ringers, with every report of a marked bird adding to our understanding of the success of the various projects. In each case, hopefully there will be enough money to deploy dedicated fieldworkers to monitor what happens to the released birds during the crucial first few weeks of independence, so that fledging rates can be accurately assessed, and to monitor return rates in subsequent breeding seasons. For slow-maturing birds, this follow-up work will involve a five-year commitment.

Maximising effectiveness

The work being funded by Natural England in East Anglia is expensive. It will be judged as successful if released birds augment local populations, whether these be in East Anglia (as hoped) or in another part of lowland England. If birds choose to breed in the North of England, where numbers are still high, or even overseas, then that may make it difficult to justify the expense of further rearing and monitoring work.

There is a concern that head-starting will be seen as a solution to the problems being faced by Curlew. It isn’t! The estimated shortfall in fledged chicks is 10,000 birds per year, across the whole of the UK, and head-starting will never make a big impact on that number. It may be a way to boost numbers in lowland areas, from which the species would otherwise be lost, but only if the conditions for successful breeding can be created and maintained. This means tackling the thorny problems of habitat degradation and predator numbers. Head-starting may seem like a dynamic intervention but if birds are released into areas where breeding success is too low then it’s not going to produce a sustainable solution to the problems being faced by England’s Curlew.

*Photos of ringed birds are particularly appreciated*

The Norfolk head-starting project would appear to tick all the right boxes – release sites with low predator numbers, right next to an estuary with lots of Curlew and with successful breeding sites near-by. Head-started birds soon start to explore the mixture of arable and tidal resources available to them and it looks as if early-years survival rates might be as high as expected of wild-reared birds. Despite all these positive signs, it will be a couple of years until this year’s young Curlew start breeding – somewhere – and that will be the crucial test of head-starting. Meanwhile, it is hoped that birdwatchers will look out for colour-ringed birds, so that survival rates can continue to be monitored. Every Curlew counts!

Norfolk-ringed head-started Curlew wear yellow flags, each with number & letter, immediately above an orange ring. Please report sightings of colour-ringed head-started Curlew using THIS LINK.

When mates behave differently

August 7, 2022November 7, 2022 / Graham Appleton / 8 Comments

Iceland’s 40,000 Oystercatchers are an interesting mix of resident birds and migrants, providing an ideal system in which to study the costs and benefits of the two options, and to try to work out what influences whether an individual becomes a ‘resident’ or a ‘migrant’. I’ve added the inverted commas because many residents migrate within Iceland in spring and autumn; it’s just that they don’t undertake long-distance flights across the Atlantic.

In their paper in Ecology & Evolution, Verónica Méndez and colleagues from the South Iceland Research Centre (University of Iceland), the University of Aveiro (Portugal) and the University of East Anglia (UK) investigate the timing and success of breeding attempts by resident, migratory and mixed (resident/migratory) pairs of Icelandic Oystercatchers.

Iceland’s Oystercatchers

As outlined in Mission Impossible: counting Iceland’s wintering Oystercatchers, about 30% of Icelandic Oystercatchers never leave the country, coping with cold temperatures, short December and January days and a restricted diet. In the winter months they can be found in the tidal zone of a few estuaries, mostly in the warmer west.

The majority of Iceland’s Oystercatchers fly 1000 km or more across the Atlantic, to Ireland, the UK and the coastal fringe of western Europe. Here, many colour-ringed birds have been spotted by birdwatchers, who play a vital part in migration studies. The blog Which Icelandic Oystercatchers cross the Atlantic? revealed that males and females were equally likely to migrate, while there appeared to be no assortative mating in spring (residents don’t preferentially choose resident partners, for instance).

It would be easy to envisage circumstances in which resident birds might be at an advantage, at the start of the spring breeding season, having not had to cross the Atlantic and thus being ready if an early nesting opportunity opens up. On the other hand, in a cold spring or after a particularly harsh winter, perhaps they could be in poorer condition than newly arrived migrants, and this may potentially delay breeding. What actually happens?

Fieldwork

Both resident and migrant Oystercatchers breed throughout lowland Iceland. Within breeding pairs, it is estimated that about 20% of pairs are resident, 46% are migrant and 34% are mixed. These are long-lived birds that generally maintain the same partners between years, despite the fact that individual males and females may spend seven months of the year up to 3000 km apart. Parents tend to be equally involved in incubation duties, territorial defence and chick rearing, although males tend to remain with their youngsters longer than do females.

Between 2015 and 2018, Verónica Méndez and her colleagues monitored the breeding attempts of Oystercatchers in southern Iceland, continuing a study of marked individuals that started in 2013. Adults were caught on the nest and sexed by later analysis of feather samples. With the help of a network of volunteer observers, the winter locations of 186 (out of 537) marked birds had been established when the paper was first written. Using these known outcomes and with additional information from stable isotope analysis, it was possible to assign the remaining 351 birds as ‘residents’ or ‘migrants’. Amazingly, 73 of these 351 birds have been seen since the isotope data were analysed and all of the assumptions on winter locations were found to have been correct.

*Early nesting attempts may be hampered by spring snowfall*

The first migrant Oystercatchers arrive in Iceland in February but no nesting has been recorded before mid-April. Searches for colour-ringed birds and nests were conducted every 2-3 days and then nests were followed through to hatching or failure. Second (and third) nesting attempts were also monitored. Oystercatchers remain in the vicinity of the nest after hatching their chicks and then feed them throughout the growing period. Chicks were metal-ringed just after hatching and individually marked with colour-rings when around two weeks old. Families were monitored every 3-4 days until all chicks were fledged or lost, allowing productivity (number of chicks fledged per pair) and fledging success (number of chicks fledged in nests where at least one egg hatched) to be recorded.

Who breeds when?

Verónica and her colleagues were able to estimate laying dates for 138 pairs with known migratory behaviour (56 migrant, 50 mixed and 32 resident pairs) in one or more seasons during 2015-2018, providing a total of 228 observations.

The top graph shows that, on average, 2015 was a much later breeding year than the other three. This was a colder spring; the sort of colder conditions that an older Oystercatcher may well have encountered frequently in its youth! (The longevity record for BTO-ringed Oystercatcher is 41 years – see Waders are long-lived birds – and the trend for there to be more frequent warmer springs is discussed in this Black-tailed Godwit blog).

The lower graph shows a breakdown of the data into the three categories – Resident (black dots), Mixed (grey) and Migrant (white). There is no difference between the egg-laying dates for residents across the four years. However, in the 2015 breeding season, in cases where either member of the pair is a migrant, there was an average nesting delay of over a week. An analysis in the paper shows that it does not matter which member of a mixed pair was the migrant, the delay in 2015 was the same.

Reproductive performance

*Unusually amongst waders, adult Oystercatchers feed their chicks*

As expected, Oystercatcher pairs that made earlier nesting attempts were more likely to lay a replacement clutch after nest loss, had higher productivity and higher fledging success. This is in line with the modelling paper described in Time to nest again. Early-nesters tended to have bigger clutches too. Any differences between the performance of residents, mixed pairs and migrants could be accounted for just by the timing of nest initiation.

In the papers’ Discussion, the authors suggest that, in the three warmer years, earlier nesting of pairs that included at least one migrant was sufficient to slightly enhance nest success but not overall productivity, above that achieved by pairs with residents. The migratory behaviour of the male within a pair appeared to have a stronger effect on fledging success than the migratory behaviour of the female, suggesting that males may play a more important role than females at the chick stage. This is interesting in the context of previously-published research by Verónica and her colleagues, as described in The Dad Effect blog.

What does this all mean?

In other studies, described in the Discussion, residents in systems where some individuals migrate have been found to have advantages over migrants, because they can get on with breeding earlier. This was not the case for Icelandic Oystercatchers, potentially because migrants can arrive in good condition in all but the coldest of years.

In the cold year of 2015, Oystercatcher pairs nested an average of between a week and 12 days later than in other years. This delayed nesting occurred in migrant and mixed pairs but not in resident pairs, suggesting that the effect of the severe weather may have been greater on migrants than residents. Cold spring conditions in Iceland tend to be part of a wider pattern of cold weather across northwest Europe. The authors suggest that wintering conditions might influence the body condition required to reproduce and that these conditions may be more variable for migrants.

Only one cold year occurred during this study, so the authors don’t know whether pairs with migrants consistently breed later in colder years. Given that cold springs are increasingly rare in Iceland, 2015 may turn out to have been one of the few remaining opportunities to reveal the dynamic nature of links between weather, migratory behaviour and breeding phenology at these latitudes.

One potential explanation of the difference in the timing of nesting is the effect of habitat. The Icelandic team has found that there is a strong tendency for migrants to breed inland, whereas residents tend to breed along the coast. During the cold spring of 2015, inland habitats were not available as early as in the following years (everything was frozen), mostly delaying the breeding attempts of migrant and mixed pairs, rather than residents pairs.

Long-term studies

*Verónica Méndez with one of the marked birds*

The take-home message of the paper by Verónica Méndez and her colleagues is that it pays to nest early, which is not unexpected. Perhaps it is surprising that, in the cold spring of 2015, mixed pairs still bred at the same time as pairs of migrants, suggesting that residents waited for their migrant partners. Perhaps, the benefits of nesting with the same partner are very strong, or finding an alternative mate is difficult or both?

The study suggests that the links between individual migratory behaviour and reproductive success can vary over time and, to a much lesser extent, with mate migratory behaviour. Understanding these effects of pair phenology on breeding success may help researchers to understand the potential impacts of changing environmental conditions on migratory species. Such variation is very difficult to capture unless long-term funding is available. Four years may seem like a long time to observe the same Oystercatchers but, for birds that may easily live twenty years, this is nothing!

The full paper can be found here:

Effects of pair migratory behaviour on breeding phenology and success in a partially migratory shorebird population. Méndez V., Alves J.A., Gill, J.A., Þórisson, B., Carneiro, C., Pálsdóttir, A.E., Vignisson, S.R. and Gunnarsson, T.G. Ecology & Evolution

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