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*

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.

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

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

January to June 2022

June 25, 2022July 13, 2022 / Graham Appleton / 1 Comment

Here are brief summaries of the first nine WaderTales blogs of 2022. 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! I have not covered every new paper; perhaps your favourite is in the pipeline or perhaps I did not happen to spot it? The blogs are described in order of publication.

Welsh Oystercatchers

To explain 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). 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 but what happens when Oystercatchers can’t find food? This paper makes a strong case for the protection of networks of sites, so that individuals have alternatives when needed.

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.

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!

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!

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.

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.

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. It was a good excuse to round up the Whimbrel stories in other WaderTales blogs, as you can read in Whimbrels arrive in Iceland.

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 of 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 and conservationists.

Conflict with forestry

Just a few days later, Aldís Pálsdóttir’s second paper was published. By mapping distributions of breeding waders in the vicinity of forests, she 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. It should be noted that three-questers of Europe’s Whimbrel nest in Iceland, as well as half of the Golden Plover and Dunlin. 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.

Blogs from previous years

WaderTales blogs in 2021

WaderTales blogs in 2020

WaderTales blogs in 2019

WaderTales blogs in 2018

WaderTales blogs in 2017

Whimbrels arrive in Iceland

April 27, 2022December 29, 2022 / Graham Appleton / 5 Comments

There is something magical about standing in Eyrarbakki in South Iceland, in spring, watching small flocks of Whimbrel come in over the sea. Thanks to geolocators and satellite tags (about which more later) we know that these amazing waders will have been in the air for around five days, since leaving the west coast of Africa.

Looking down at the seaweed-covered rocks on the morning of 27^th April 2022, we could pick out small groups of new arrivals. Most were resting but one bird was looking for crabs, just as it had been doing in West Africa just a few days previously. A few birds headed off inland while we were watching, making the distinctive seven-note whistle as they left. It sounded almost like a cry of “made it”!

Setting the scene

We had been here before. On 22^nd April 2008, I did a live broadcast for the BBC Radio 4 programme World on the Move from this very spot, when I described visible migration to Brett Westwood. On that day, we could see Purple Sandpipers and Turnstone feeding on the tide edge, White Wagtails and Meadow Pipits, newly arrived from Iberia, and small flocks of Golden Plover flying in low over the sea. During the programme, a gaggle of 35 Pink-footed Geese flew in strongly from Britain, as did four Arctic Skuas that had spent winter in the Southern Hemisphere. You can listen to the programme HERE.

On 27^th April 2022, the skies were not as busy as they had been fourteen years previously. High pressure over the British Isles and northerly winds across the Atlantic seemed largely to have pressed ‘pause’ on migration from Britain & Ireland. There were small numbers of newly-arrived White Wagtails, Meadow Pipits and Black-headed Gulls feeding on insects emerging from the banks of rotting seaweed, but the stars were definitely the Whimbrel.

These banks of seaweed will be even more important in May, when there will be hundreds of waders refuelling for the next leg of their journeys, with Sanderling and Dunlin on their way to Greenland and some Knot and Turnstone perhaps flying as far as northeast Canada. When the tide is high enough to wash maggots out of the seaweed, you can sometimes see Red-necked Phalaropes along the tide-line, spinning around and picking food off the surface of the water.

Whimbrel migration

We knew that the Whimbrel were on their way because Global Flyway Network had published a map showing the location of ‘Acuno’, a bird wearing a satellite tag that was put on in the Bijagós archipelago of Guinea Bissau. It had been logged west and north of Ireland on the previous evening, already 6000 km and 4 days into its migration. Doing the sums, it seems unlikely that it could have reached Eyrarbakki by the time that we were there but perhaps it flew past soon after, sending signals back to mission control that would confirm arrival**.

** An hour after I published this blog, Acuno was found to have diverted to the Faeroes. It may breed there – as many Whimbrel do – or if could have run out of fuel and landed there, to put on some extra grammes of fat. We’ll see whether it resumes migration.

** Three weeks later, Acuno flew to Iceland. How much will it have been disadvantaged by giving up on direct flight?

Only a minority of Whimbrel fly straight from Africa to Iceland in spring although almost all fly directly south in the late summer. Most individuals spend late April and early May in Ireland, the UK or on the west coast of mainland Europe. Ireland is by far the most important staging area. The individuals on Eyrarbakki beach may have been tired but there could be advantages to being an early bird. See Time to nest again? based on a paper by Morrison et al.

There are several WaderTales blogs about Icelandic Whimbrels:

Whimbrels on the move summarised the movements of Icelandic birds, based on reports of ringed and colour-ringed individuals. In the paper upon which the blog was based (Gunnarsson & Guðmundsson) there was a strong suggestion that birds only stop off in Britain & Ireland on the way north. Geolocator-based research by Alves et al showed that at least some birds were flying straight from Iceland to West Africa and that these sea-crossings could be very rapid.

Migrations to and from Africa were investigated further in a paper by Camilo Carneiro et al that was summarised in Iceland to Africa, non-stop. More recently, papers by the same team have shown that the most consistent point of the annual migration story is departure from Africa and discussed the links between weather and phenology. These two papers have appeared as the WaderTales blogs – Whimbrel: time to leave and A Rhapsody of Whimbrel.

The latest blog about this research is Winter conditions for Whimbrel, based on a paper that assesses the influence of winter conditions on subsequent breeding performance.

Searching for Black-tailed Godwits

We had seen a flock of eight Whimbrel, earlier in the morning, when we were checking fields for colour-ringed Black-tailed Godwits. The Whimbrel were gliding into land, about five km from the coast, before seeming to melt into a patch of rough grassland, bleached after winter frosts.

We did not pay the Whimbrel much attention as, on the other side of the road, there were Black-tailed Godwits probing for worms in silage fields that were already green, after a few days of warmth and the liberal addition of fertilizer. This is our target species during spring trips to Iceland. We have discovered that the arrival time of individuals is remarkably consistent from year to year, which initially seemed surprising, given that migration appears to be getting earlier. There is more about this in Why is spring migration getting earlier? based on a paper in Proceedings of the Royal Society B.

One of the fascinating things about visiting Iceland is that no two years are the same. 2022 has been a dry, warm spring, with northerly winds potentially delaying migration from Britain and Ireland, as mentioned earlier. Early-arriving Black-tailed Godwits that were wearing colour-rings were birds that winter in Portugal and France and migrate via the Netherlands. There was a period of helpful winds for these early birds that fly further but get to Iceland earlier. This strategy is discussed in the blog Overtaking on Migration, based on a paper in Oikos.

Looking forwards

The short Icelandic summer provides fantastic conditions for these waders to raise their chicks, although there are concerns as to how agricultural development, increased forestry and infrastructures will affect these species in the future. In June, in just two months’ time, adults will cross the Atlantic. Black-tailed Godwits head for the British Isles and the west coast of continental Europe and Whimbrel will return to West Africa. By August, the next generation will be preparing for the journey south and we will be here in future springs to monitor their return to Iceland.

Navigating a vast ocean

March 15, 2022 / Graham Appleton / 4 Comments

The journeys that shorebirds make, as they cross the oceans of the globe, are truly remarkable. Individual birds demonstrate amazing endurance and navigational expertise while in the air for days at a time. Satellite transmitters are providing opportunities to understand how shorebirds refine their flight plans in responses to the wind patterns they encounter. In a paper in Movement Ecology by Jenny Linscott and colleagues, we join the northward flight of Hudsonian Godwits across 7,000 km of the Pacific Ocean and the Gulf of Mexico.

Coping with wind

Conditions encountered en route can dramatically impact the energy that migratory species spend on movement. To complete their journeys across barriers such as oceans, migratory birds need to manage energetic costs by adapting to the wind conditions they encounter. It’s a dynamic environment; no two years are the same and there is often little relationship between local conditions upon departure and what lies ahead, as for instance discussed in the WaderTales blog Rhapsody of Whimbrel.

*Migrating Hudsonian Godwits are* *heading for Alaska*

If an individual bird has full knowledge of its location at all times and a fixed destination point in mind, then perhaps it can adjust its airspeed and direction of flight so that it can completely compensate for any lateral drift that is caused by the wind systems en route. Alternatively, it might accept the drift that it experiences or only partly compensate, perhaps gambling that there may be systems ahead that might cause drift in the other direction. It may even over-compensate for the wind patterns it experiences at a particular time, which may be a good idea if there is more of the same weather to come. The authors of the Hudsonian Godwit study explain how these different approaches may integrate to create a movement strategy and summarise what has been found in other studies. Interestingly, it has been suggested that complete compensation (continually adjusting the flight-plan) might not be possible for trans-oceanic flights because there are no landmarks to use as reference points.

Hudsonian Godwits spend the austral summer in coastal Chile and Argentina and migrate northwards in spring, through the midcontinental United States, to breed in subarctic Alaska and Canada. For birds taking off from Chiloé Island in Chile, the first part of the journey takes them across the open Pacific Ocean, the relatively narrow landmass of Central America and the Gulf of Mexico. Godwits making this flight have few or no opportunities to stop, and they traverse several global wind regimes that differ in directionality and strength along the way. The authors predicted that birds would experience drift during their journeys, especially over the featureless open ocean, and increase compensation as they approach North America. Given the vast distances and time spent in flight, it might be expected that the winds experienced during flight should influence the points where individuals cross the coast into North American airspace.

*Flock of Hudsonian Godwits on Chiloé Island in Chile – a long way from Alaska*

Tracking transoceanic journeys

During the springs of 2019, 2020 and 2021, Jenny Linscott used satellite tracking devices to follow Hudsonian Godwits, as they migrated northward across more than 7,000 km between Chiloé Island, Chile and the northern coast of the Gulf of Mexico.

Prior to migratory departure, two types of solar-powered satellite transmitters were deployed on a total of 54 adults. Technical details are provided in the paper, alongside information as to how the data were filtered and interpreted. This paper focuses on the journey across the Pacific Ocean and the Gulf of Mexico, as birds head towards a relatively narrow refuelling area in North America (the eastern parts of Kansas, Nebraska, South Dakota, and North Dakota).

For any two points along each bird’s route, between Chiloe and the coast of the Gulf of Mexico, it was possible to calculate distance travelled, ground speed, turning angle, and heading. Having removed low-quality data, the team were left with 29 tracks and 689 locations with which to work. They linked each location with the range of possible wind conditions that godwits were likely to be experiencing at the time, depending upon flight height. They then “calculated the total magnitude and mathematical direction of the wind flow for each location at each altitude using vector trigonometry”. Previous studies have shown that migrating waders change altitude in order to find better wind conditions, allowing the team to assign the most likely wind conditions to each godwit location. Please see the paper for details of the modelling and assumption-testing processes.

Results

A total of 24 complete and 5 partial northward journeys were collected from birds migrating north, including repeat tracks from two individuals, which were followed for three years. The sample size was reduced by device failure/malfunctions, presumably some mortality, and by eight birds that oversummered in Argentina (see Teenage Waders and Gap year for sandpipers for information about oversummering shorebirds). The 25 birds in the study comprised 14 males and 11 females.

Godwits for which there were complete tracks undertook continuous flights lasting about six days, covering an average of 8,361 km, before making their first stops.
Godwit ground speeds were best predicted by a strategy in which individuals flew at the altitude offering the most wind support in the preferred direction of movement, but were restricted to altitudes at or below 3000 m. It seems likely that the godwits were mostly flying between 100 m and 750 m above sea level.
Tracked godwits travelled along paths which showed a close match to a Great Circle line from Chiloé to the North American target area.
When flight behaviours were analysed, full compensation was the most frequent behaviour, accounting for 41.1% of all observed flight segments. Fewer segments were associated with partial compensation (23.5%), tail winds (8.1%), full drifting (9.4%), or overcompensation (16.0%).
The prevalence of full compensation remained constant across wind conditions. For example, full compensation was the dominant behaviour under crosswinds to the east (32.0%) and west (45.3%). Full compensation was also prevalent across regions, comprising the largest proportion of behaviours exhibited over the Pacific Ocean (45.1%), while crossing Central America (23.9%), and in the Gulf of Mexico (31.4%).
There was considerable variation in migration patterns over the Gulf of Mexico and it is suggested that some birds may have been running out of fuel and heading for the nearest land.
One individual tracked repeatedly over three years completed its crossing of the Gulf of Mexico in central Texas every year. The other bird tracked for three years had no specific point at which it crossed the coast but always ended up in the same spring staging area.

Jenny Linscott and colleagues found little support for their prediction that godwits would tolerate more drift early in their flight and gradually begin to increase compensation as they approached North America. Instead, both fully supported flight (benefiting from tail winds) and full compensation were common soon after leaving Chiloé. Compensation did not increase with distance travelled, was not constrained during flight over open ocean, and did not influence where an individual ultimately crossed over the northern coast of the Gulf of Mexico, at the end of this flight. Instead, the team found a strong preference for full compensation throughout godwit flight paths. Birds ‘knew’ where they were along their route and could judge how to adjust their headings so as to compensate for the drift they were experiencing at any given time. The paper’s Discussion includes more detailed consideration as to how compensation appeared to operate in different parts of the journey and in different wind conditions.

How do shorebirds, flying over the vastness of an ocean ‘know’ where they are, with no island landmarks? Are individuals within migrating flocks picking up on changes in temperature or humidity, that mark passage through broad wind regimes, can they navigate with reference to sun position and stars, are there magnetic cues, or can they interpret surface swell patterns? Perhaps it’s a mixture of several of these skills? It’s pretty amazing!

Learning more

Jenny Linscott and her colleagues found that fully compensating for wind displacement appears to be a critical strategy for Hudsonian Godwits making a long-distance, transoceanic flight. While godwits often followed wind flow in the early stages of this journey, they nonetheless engaged in full compensation more frequently than any other behaviour during the entirety of the flight, across a vast and apparently featureless ocean. These continuous adjustments help to make sure that birds can fly extremely long distances without running out of energy. The team wonder how well future generations will cope with changing wind systems over warmer seas.

The full paper can be found here:

Compensation for wind drift prevails for a shorebird on a long-distance, transoceanic flight. Jennifer A. Linscott, Juan G. Navedo, Sarah J. Clements, Jason P. Loghry, Jorge Ruiz, Bart M. Ballard, Mitch D. Weegman, and Nathan R. Senner. Movement Ecology. https://doi.org/10.1186/s40462-022-00310-z

The Hudsonian Godwits studied here are flying 7,000 km north across the Pacific, but this pales into insignificance when compared to Bar-tailed Godwits that commute between Alaska and New Zealand. The Pacific was once considered a barrier to migration but it is increasingly seen as a conveyor belt. There is an excellent review article by Theunis Piersma and colleagues in Ornithology, the title of which explains its content:

The Pacific as the world’s greatest theater of bird migration: Extreme flights spark questions about physiological capabilities, behavior, and the evolution of migratory pathways. Theunis Piersma, Robert E Gill, Jr, Daniel R Ruthrauff, Christopher G Guglielmo, Jesse R Conklin and Colleen M Handel. Ornithology, https://doi.org/10.1093/ornithology/ukab086

How many shorebirds use the East Asian-Australasian Flyway?

February 10, 2022February 14, 2022 / Graham Appleton / 7 Comments

The level of threat facing a shorebird species is assessed using a set of criteria that tries to answer three key questions: How many breeding pairs are there? How quickly are numbers falling? and How restricted is the distribution? In a paper published in Ibis at the end of 2021, Birgita Hansen and colleagues produced population estimates for 37 species of shorebird on the East Asian-Australasian Flyway, for which the non-breeding distribution includes Australia and New Zealand. This new study shows that there are at least nine million shorebirds on this flyway. How many more would there have been ten, twenty or fifty years ago?

Population estimation

*More comprehensive data are now available for countries such as Myanmar*

This is a good time to attempt to assess population sizes of shorebird species on the East Asian-Australasian Flyway because the quality of the data available is so much better than it was even ten years ago. Increased cooperation across borders, fostered through individual efforts by concerned birdwatchers, by conservation NGOs and through bodies such as the East Asian-Australasian Flyway Partnership, has delivered reliable counts of shorebirds in previously inaccessible areas, especially around the Yellow Sea.

The East Asian-Australasian Flyway covers an area of 85 million square kilometres, from Russia and Alaska, in the north, through to Australia and New Zealand in the south. Birgita Hansen and colleagues have revised the population estimates for 37 migratory shorebird species protected under Australian national environmental legislation. Population estimates were generated by:

Summarising existing count data in the non-breeding range
Extrapolating the data to try to include the numbers of birds using uncounted areas and
Modelling abundance on the basis of estimates of breeding range and density.

This was not just a number-crunching exercise; expert opinion was sought, especially to refine estimates for species with low data quality.

*Flocks of roosting shorebirds on the white sand of Eighty Mile Beach in Western Australia*

The main count data available to the authors came from the Australian National Shorebird Monitoring program (formerly Shorebirds 2020), the Queensland Wader Study Group, the Ornithological Society of New Zealand, and the Asian Waterbird Census. Two major strengths of the paper are a clear explanation of the methods used to create the population estimates and open consideration of the quality of the estimates. The authors explain how it is possible to produce population estimates in areas where there are significant gaps in the data. These features will be important to teams making future assessments of numbers.

The Hansen paper builds on previous estimates by Bamford et al, in a paper published in 2008, that used data collected between 1986 and 2000, and through an expert-assessment process (Wetlands International 2012). However, the various estimates have been derived in different ways and cannot directly be compared.

There is a summary of the Hansen population estimates on the Department of the Environment (Australia) website. Context and caveats are provided in the new paper.

How many shorebirds?

Species that form coastal flocks in a relatively well-established set of sites are easier to census than others that are spread thinly or across a range of habitats. Flyway counts of Curlew Sandpiper are thought to include almost all of the sites used by the population, so a total of 85,086 is adjusted to an estimate of 90,000 to account for gaps. For Latham’s Snipe, the flyway estimate is 35,000, based on the breeding range and density estimates, but actual flyway counts only total 1124. For Curlew Sandpipers, non-breeding season numbers appear to be reliable indicators of population size but for Latham’s Snipe breeding season estimates are more realistic. Variability in data quality is not unusual; the British & Irish estimates of winter numbers of Common Snipe, Jack Snipe, Eurasian Woodcock, Golden Plover and Northern Lapwing are similarly imprecise, as discussed in Do population estimates matter? and Ireland’s wintering waders.

Estimates of population size obtained through analyses of breeding ranges and density indicated that non-breeding counts for 18 species in the Hansen study were relatively uncertain. Breeding ground estimates were considered the best available data for ten species that mostly use poorly-surveyed freshwater and marine habitats, especially in south-east Asia, or are thinly distributed on the open coastline in the non-breeding season. The WaderTales blog Waders on the coast reflects on the latter issue for UK waders.

Birds at risk

Prioritisation of conservation action for shorebirds is underpinned by the threat levels assigned to them. This means that it is probably easier to access funding for Critically Endangered Spoon-billed Sandpipers than for Near Threatened Curlew Sandpipers. There are three categories indicating imminent risk of extinction in the IUCN Red List – Critically Endangered, Endangered and Vulnerable. The definition of each level is set out on this page from BirdLife.

This flock of Far Eastern Curlew has just been spooked. Disturbance is a major issue at some key sites. Julie Keating won Environmental Citizen of the Year for her work in supporting shorebirds in Port Hacking (NSW)

Several of the wader species on the East Asian-Australasian Flyway that are most at risk, such as Nordmann’s (or Spotted) Greenshank and Spoon-billed Sandpiper, are not included in the review by Hansen et al. because they do not generally migrate as far south as Australia (but there is a WaderTales blog called Spoon-billed Sandpiper: track and trace).

Two species that winter in Australia in significant numbers are categorized as Endangered by IUCN – Far Eastern Curlew and Great Knot. When comparing the Hansen estimates (mainly based on data from 2011 to 2016) with Bamford et al (data from 1986 to 2000), the population of Far Eastern Curlew is now assessed to be lower (35,000, as opposed to 38,000), while the population of Great Knot is now thought to be bigger than previously realised (425,000, as opposed to 375,000). This does not mean that numbers have gone up – we know that annual counts at key sites have fallen significantly – it indicates a more comprehensive estimate of numbers, particularly in uncounted areas.

Indeed, as shown by Colin Studds et al, summarised in Wader declines in the Yellow Sea, both Far Eastern Curlew and Great Knot numbers have been declining at an alarming rate for two decades. The fact that the drop in Far Eastern Curlew numbers is less striking than might have been expected and that there is an apparent increase in Great Knot numbers reflects more comprehensive counts from what are now known to be important sites along the flyway. The increased figures do not mean that the two species are any less threatened!

Seven species considered in the Hansen paper are listed as Near Threatened. Estimates of Grey-tailed Tattler and Red-necked Stint have been raised, from 50,000 to 70,000 for the tattler and from 325,000 to 475,000 for the stint. There is no change in the estimate of Bar-tailed Godwits (325,000), despite significant declines in numbers in Australia, again reflecting the discovery of significant numbers in sites where they were previously unrecorded or under-recorded. The Black-tailed Godwit estimate remains at 160,000.

The estimates of two Near Threatened species have dropped alarmingly, despite more comprehensive information on the sites that they use. Red Knot and Curlew Sandpiper numbers have halved (220,000 down to 110,000 and 180,000 down to 90,000, respectively).

Cautionary tale

The figures in the Hansen paper are based on the best available information for the period up until 2016. The welcome, increased focus upon shorebird conservation issues throughout the flyway is uncovering new and better count data. Birgita shared the following cautionary tale about the Near Threatened Asian Dowitcher, the population estimate of which is given as 14,000 in the paper, somewhat lower than the estimate of 24,000 that was published by Bamford et al in 2008.

“In 2019 there was a count of 22,432 Asian Dowitchers at Jiangsu Lianyungang, on the Chinese coast, which was interpreted as being 97.5% of the global population at the time (based on Bamford). This figure well exceeded our 2016 estimate of 14,000, clearly indicating that, despite access to greater volumes of data through the Asian Waterbird Census, there was a substantial number of dowitchers that had been missed in standard monitoring. So we can see already how, even with the extrapolations we used, the numbers can be highly uncertain.”

Population estimates are only estimates – the clue is in the name – but it is important to work out, as best as possible, how many birds there are, in order to assess the vulnerability of individual species and the importance of the sites that are used by assemblages of shorebirds. When 1110 Curlew Sandpipers were counted at Broome (Western Australia) in 2021, that was over 1% of the reduced flyway total of just 90,000 – and that’s important. Similarly, 4674 Bar-tailed Godwits in Tasman Bay (New Zealand) in 2021 exceeds the 1% threshold for the species and an amazing count of 9810 Sharp-tailed Sandpipers at Lake Martin (Victoria) in 2019 represents 11.5% of the 85,000 estimate in the Hansen paper. There are many more examples.

This population information is complementary to regular counts at key sites, that track population trends, and colour-ring observations that monitor annual survival rates of adults (there is a WaderTales blog about this – Measuring Shorebird Survival).

*Shorebirds at Jiangsu, on the Yellow Sea coast of China – now a conservation area*

More details

In the Ibis paper, Birgita Hansen and her colleagues discuss the rationale and limitations of the approaches they have used to obtain population estimates and how their methods could be used in other situations. Data available for population estimates will always vary in quality and extent among species, regions and migration stage, and approaches need to be flexible enough to provide relevant information for conservation policy and planning. Anyone considering this sort of exercise would be advised to read the whole paper:

Generating population estimates for migratory shorebird species in the world’s largest flyway. Hansen, B.D., Rogers, D.I., Watkins, D., Weller, D.R., Clemens, R.S., Newman, M., Woehler, E.J., Mundkur, T. and Fuller, R.A. Ibis. DOI/10.1111/ibi.13042

New Bar-tailed Godwit Subspecies

October 18, 2021October 18, 2022 / Graham Appleton / 6 Comments

The description of a new subspecies of Bar-tailed Godwit begs two questions, ‘How do we identify new subspecies?’ and ‘Is the concept of a subspecies helpful?’. Put simply, the answers are ‘That depends’ and ‘Yes, especially when subspecies are the focus for conservation action’.

A new study of Bar-tailed Godwits, and the proposal to identify Limosa lapponica yamalensis as a new race, usefully highlight the importance of the flyway between Siberia and the Arabian Sea and the challenges being faced by waders that use this migration route.

Limosa lapponica yamalensis

Bar-tailed Godwits breed across the whole of northern Eurasia and in Alaska. Since the last Ice Age, following glacial retreat, new breeding opportunities in northern latitudes have become available to waders. The emergence of separate migration flyways, linking wintering and breeding areas, has led to a divergence of the species into a number of distinct populations, some of which have already been defined as subspecies. In their paper in IBIS, Roeland Bom (NIOZ Royal Netherlands Institute for Sea Research) and colleagues from the Global Flyway Network argue that the taymyrensis subspecies should be further divided between those that winter in the Middle East (and presumably East and South Africa) and those that winter in West Africa. Their recommendation is based on studies of migratory behaviour, breeding area, morphology (measurements) and population genetic differentation in mitochondrial DNA. Their main focus has been a study of spatial and temporal differences in migration routes.

How many subspecies?

The most famous subspecies of Bar-tailed Godwit is baueri; these amazing birds fly directly from Alaska to New Zealand at the end of the breeding season and return via the Yellow Sea in spring. Theirs is the most impressive migration route of any wader, including non-stop flights of well over a week. These are the largest Bar-tailed Godwits.

Bar-tailed Godwits wintering in Australia are mainly birds of the menzbieri race. These breed from central Siberia across to north-east Russia and migrate north and south via the Asian coast, especially the Yellow Sea. Bar-tailed Godwits breeding further south in eastern Russia are usually described as anadyrensis, these birds are smaller than baueri but bigger than menzbieri.

Bar-tailed Godwits breeding in western Siberia have all been known as taymyrensis, named after the Taymyr** Peninsula, while those breeding in Scandinavia, Finland and the far west of Russia are identified as lapponica. Nominate Limosa lapponica lapponica birds winter in northwest Europe and most taymyrensis use the East Atlantic Flyway to winter at least as far south as Guinea-Bissau in West Africa. Taymyrensis is the smallest race. Lapponica and taymyrensis were recognised as separate subspecies two decades ago and this differentiation has been useful in discussions about Bar-tailed Godwit conservation. In the UK we see both lapponica and taymyrensis, as discussed in Bar-tailed Godwits: migration and survival.

Until now, birds migrating south from western Siberia, as far as East and South Africa, have been considered to be taymyrensis and it is these birds that have been reclassified – with the new name of yamalensis, after the region of Russia in which the subspecies breeds.

** In the IBIS paper, the authors use Taimyr (rather than Taymyr) as this is preferred by Russian co-authors. I am maintaining consistency within WaderTales.

What’s different?

The studies summarised in the IBIS paper by Bom et al are designed to test whether Pavel Tomkovich, who has studied Russia’s artic-breeding waders for several decades, was right when he suggested that taymyrensis should be split into two subspecies. (See Population structure and migratory links of Bar-tailed Godwits: Current knowledge and unsolved issues in Achievements in Studies on Waders of Northern Eurasia). Based on a small number of movements of ringed birds between areas where there are few birdwatchers, Pavel suggested that L. l. taymyrensis likely comprises two distinct (flyway) populations, one wintering in the Middle East, West Asia and East Africa and breeding on the northern West-Siberian Plain, and the other wintering in West Africa and breeding on and around the Taymyr Peninsula.

Using satellite-tracking, Roeland Bom and colleagues have now described the migration routes, breeding destinations, and annual-cycle timing of Bar-tailed Godwits using wintering areas in the Middle East (Oman) and West Africa (Mauritania and Guinea-Bissau). To understand further the extent to which the two groups are different and whether or not there is any mixing of the two populations, they also examined differences in mitochondrial DNA.

Tracking through space and time

Members of the research team attached solar-powered tags to eastern taymyrensis Bar-tailed Godwits in Oman and western birds in Mauritania, Guinea-Bissau and the Wadden Sea. 52 birds caught between 2015 and 2018 provided usable tracks; 11 birds (12 tracks) linked the western wintering/migration route to the area in and around the Taymyr peninsula, while 9 birds (19 tracks) linked the Middle East to the northern part of the West Siberian plain. To limit potential negative effects of carrying extra weight, only the largest birds were tagged, which means that all of the tags were deployed on females.

Bar-tailed Godwits from wintering areas in the Middle East staged for several days in the areas around the Caspian and Aral Seas, during both northward and southward migration. Both of these areas were already thought to be important for passage waders but analysis of tracking data emphasise the critical role they play in the annual cycle of Bar-tailed Godwits. Some birds also spent short periods of time at sites in the United Arabian Emirates, Iran and India. After leaving their breeding sites, some birds moved up to 1,000 km north, to feed in high-Arctic coastal Siberia, before embarking on southward migration.

Bar-tailed Godwits tracked from wintering sites in West Africa staged in the Wadden Sea, during both northward and southward migration, with other staging points in Spain, Portugal and France, during northward migration. From the Wadden Sea, most West Africa birds flew directly to the northern West-Siberian Plain (near or in the breeding area of the Middle East birds) before heading for the Taymyr Peninsula. All birds routinely moved north before leaving for the Wadden Sea, with many using the same fuelling areas as Middle East birds.

Although birds from West Africa and the Middle East used the same feeding areas in spring and post-breeding, the phenology of the two populations were different. The northward migration, the arrival in the staging and breeding sites and the southward migration of Middle East birds were earlier than for the West Africa birds. Some birds of the two groups could be found in the same areas in Siberia in the pre- and post-breeding staging, emphasising the fact that timing differences can be just as important as spatial separation when it comes to the evolution of subspecies. This ‘spatial overlap but with timing differences’ story is similar to that seen in limosa and islandica Black-tailed Godwits in The UK and The Netherlands, as discussed in Godwits in, godwits out: springtime on the Washes.

Body size and shape

The measurements of taymyrensis and yamalensis overlap but there is a tendency for Middle East birds to have smaller bills and longer wings than West African birds. The authors suggest that, given that the two subspecies have similar diets during the non-breeding season, the different bill structure may be related to feeding requirements during the breeding season, with taymyrensis breeding in open tundra and yamalensis breeding in forest tundra and bogs within the boreal zone. It is interesting to note that the morphological differences between the taymyrensis and yamalensis subspecies are greater than those between taymyrensis and lapponica.

Genetics

West African and Middle East birds could not be separated using genetic tools available to the researchers. The authors point out that there is very little genetic variation between the three more western subspecies (lapponica, yamalensis and taymyrensis), indicating that either these three populations may have diverged recently (i.e. well after the last Ice Age) or that there is still some (small) geneflow between subspecies. The authors dicusss this in depth, in the context of all known populations of Bar-tailed Godwits and of waders in general.

A new subspecies

Roeland Bom and colleagues conclude that the old taymyrensis taxon consists of two distinct populations with mostly non-overlapping flyways, which warrant treatment as separate taxonomic units. They argue that ‘separation in space and time’ can define separate subspecies and that these differences will become apparent before morphological (size and shape) differences develop and long before it will be possible to spot genetic differences.

*Breeding locations of tagged Bar-tailed Godwits*

Yamalensis Bar-tailed Godwits breed on the northern West-Siberian Plain including the Yamal Peninsula. Birds of the subspecies follow the Central Asian Flyway, with main stopover sites in the Caspian Sea and the Aral Sea. Satellite tracking has connected Oman with other wintering areas in the Middle East, Iran, Pakistan and West India. It is likely that some birds continue further south on the West Asian – East African Flyway, with two, earlier ring recoveries showing that the subspecies can winter as far south as South Africa.

Conservation considerations

One of the key benefits of defining yamalensis as a new subspecies is that priority setting (and hence funding) for conservation action is often defined at the subspecies level. As we learnt from Ashwin Wisvanathan and Les Underhill at the International Wader Study Group conference in 2021, the numbers of waders spending the non-breeding season at the southern extremes of the Central Asian Flyway (in India) and of the West Asian – East African Flyway (in South Africa) have declined alarmingly over the last few years.

Roeland Bom and colleagues quote population estimates for taymyrensis and yamalensis Bar-tailed Godwits of 600,000 and 100,000-150,000 respectively but these are old numbers and West African winter populations are known to be declining. It is important to establish new population estimates and trends for the two populations and better to understand the migration of yamalensis. Potentially, more satellite tracking might help to suggest where to look for wintering yamalensis along the vast coastline from the southern tip of Africa to the southern tip of India, and to identify further spring and autumn stop-over sites.

Paper

The paper in IBIS concludes with a detailed description of the subspecies Limosa lapponica yamalensis, together with measurements that separate it from other races. You can read more in:

Central-West Siberian-breeding Bar-tailed Godwits (Limosa lapponica) segregate in two morphologically distinct flyway populations. Roeland A. Bom, Jesse R. Conklin, Yvonne I. Verkuil, José A. Alves, Jimmy de Fouw, Anne Dekinga, Chris J. Hassell, Raymond H.G. Klaassen, Andy Y. Kwarteng, Eldar Rakhimberdiev, Afonso Rocha, Job ten Horn, T. Lee Tibbitts, Pavel S. Tomkovich, Reginald Victor & Theunis Piersma. IBIS.

Other WaderTales blogs about waders on the West Asian – East African flyway

Well-travelled Ring Plovers makes a link between North Africa and the furthest northeast corner of Russia, extending the reach of the West Asian – East African Flyway further east than sometimes shown on maps.

In search of Steppe Whimbrel describes the migration of Numenius phaeopus alboaxilliaris, a Whimbrel subspecies that has already been declared extinct once. The subspecies migrates between the steppes of Kazakhstan and Russia and coastal East Africa.

Following Sociable Lapwings describes the migration of this threatened species along both the West Asian – East African Flyway and the Central Asian Flyway, with some interesting thoughts about a migratory divide in a wader which exhibits relatively low philopatry.

	Graham Appleton on Conservation beyond boundaries
	Conservation beyond… on Conservation beyond boundaries
	africanbirding on Conservation beyond boundaries
	Sherry Felix on Conservation beyond boundaries
	Conservation beyond… on Generational change