Navigating a vast ocean

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 Ecologyhttps://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


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.

When Oystercatchers can’t find food

In a rapidly changing world, wintering waders face unprecedented challenges. How much flexibility is there for individuals to cope with issues such as over-fishing of shellfish stocks, habitat removal, pollution, and the effects of rapid climate warming on their food supplies?

Colour-ring records show that many wintering waders tend to be site-faithful, feeding in the same estuaries and even the same small patches year after year. This makes sense if food supplies are reliable and predictable but what happens when there is massive change in food abundance? In a 2021 paper in MEPS, Katharine Bowgen and co-authors describe the impacts of a cockle die-off in the Burry Inlet (part of the Severn Estuary in Wales) on the local population of Eurasian Oystercatchers. Their findings illustrate how important it is to protect networks of sites, rather than individual inlets or estuaries.

Assessing the options

When food supplies are low – or crash suddenly – what can birds such as Oystercatchers do? There are three likely options in these circumstances:

  1. Wait and hope
  2. Move elsewhere and never return
  3. Move elsewhere until conditions improve
When food availability is low, some Oystercatchers may not complete wing moult

If ‘wait and hope’ is the main option then, following an event that reduces food availability or abundance, there should be little evidence of birds dispersing, measures of annual survival might be depressed for a period and, once conditions improve in the area, young birds might be likely to fill the spaces available. This should lead to higher proportions of sub-adults in the period immediately after such a hiatus and a steady increase in numbers.

Movements to other sites, whether temporary or permanent ought to be detectable from mid-winter counts and through reports of ringed birds. The pattern after a permanent shift in birds would be similar to that following mortality; again, young birds might be expected to take advantage of food resources as they recover In reality, of course, individual birds that use a site may opt for any one of the three options, creating a mixed picture.

Oystercatcher numbers

Over recent decades, numbers of Eurasian Oystercatchers have declined. In 2015 the species was reclassified as “Near Threatened” on the IUCN’s Red List (Birdlife International) and “Vulnerable” within Europe. It is also Amber listed on the UK’s Birds of Conservation Concern list, due to its European status, the concentration of its wintering population in protected sites and the international importance of UK breeding and wintering populations.

Colour-ring sightings can improve survival estimates

The changes in Burry Inlet Oystercatcher numbers should be viewed within a pattern of national declines. Since the 1990s, winter numbers on UK estuaries have dropped by a third, back to levels seen in the 1970s. Patterns around Great Britain vary (see below); Welsh numbers on estuaries, as assessed by WeBS, have held up well but there has been a 25-year period of decline in England and there was a sudden fall in Scottish numbers at the start of this century.

The Burry Inlet

The intertidal mudflats of the Burry Inlet in south Wales are of international importance for non-breeding waterbirds of various species, including the Eurasian Oystercatcher. This SPA (Special Protection Area) is part of The Carmarthen Bay and Estuaries SAC (Special Area of Conservation). Burry Inlet received significant conservation attention back in the 1970s, when the UK government gave permission for 10,000 Oystercatchers to be shot, to protect cockle stocks. This decision was taken despite the objections of conservationists in the UK and Norway, the latter being the summer home of many of these birds. The fact that cockle numbers continued to fall after the cull was an embarrassment, suggesting that Oystercatcher predation was not the only factor at play. Fast forward another 25 years, to the start of the period considered in this paper …

The cockle population in the Burry Inlet SPA declined from 1997 to 2004, before an abrupt ‘crash’ in stocks between 2004 and 2010 which was linked to increased mortality in older cockles, which are particularly important to commercial shellfishers. There are suggestions that losses were associated with warmer summers and sewage releases in periods of wet weather. While there has been some recovery since that period, stocks of larger cockles are still very low.

As cockles are a major prey species for Oystercatchers, the loss of larger individuals may place significant pressure on their populations, as has also been seen in the Dutch Wadden Sea and in The Wash SPA in the UK. Studies in the latter area, by BTO scientists and using data from the Wash Wader Research Group, linked declines in Oystercatcher survival and numbers to years of low cockle numbers (Atkinson et al. 2003 and Atkinson et al. 2005).

When trying to understand Oystercatcher responses to cockle changes in the Burry Inlet and the wider Carmarthen Bay SAC, Katharine Bowgen and colleagues had two main data-sets available to them. The Wetland Bird Survey, and the Birds of Estuaries Enquiry that preceded it, have provided fifty years of data on winter numbers for the Burry Inlet and other local and regional sites. The relative importance of different areas within Carmarthen Bay and the Burry Inlet were established using Low Tide Counts (see below).

Ringing operations also contributed data on the movements of marked birds, individual body masses that could be used to assess the condition of trapped birds, retrap information from which survival rates can be estimated, and opportunities to assess how many juveniles and immatures there are within samples of caught birds. November estimates of cockle biomass were available for the period from 1993 to 2008 (NRW/CEFAS).

What happened to Burry Inlet Oystercatchers?

Here are some of the key findings. Please see the paper for methods and full results. The study was funded by CCW (now NRW).

Extracting Oystercatchers from the cannon-net, having made a successful catch
  • Adult Oystercatchers were found to be in better body condition than immatures and juveniles. Non-breeders may spend three or more years in sites such as the Burry Inlet before first returning to breeding areas.
  • There was considerable variation in annual body condition indices. Two features stood out. Condition was lower in 2005, the winter following the crash in cockle stocks, and improved in the following year. A similar bounce-back could be seen after a particularly cold winter (2010).
  • From recapture data, apparent survival post-2000 was positively correlated with total cockle biomass. Apparent adult survival dropped from an average of 99.3% (range 98.3-99.9%) to 78.5% (range 68.5-84.3%) during the years following the crash in cockle stocks (2004), before rising back to 99.5% (range 99.0-99.9%).
  • In a previous BTO report to CCW (Niall Burton, Lucy Wright et al, 2010) the survival impacts of the Burry cockle crash appeared higher. This effect was diluted with the addition of eight extra years of data presented in this paper. Shorter snapshots of data do not fully capture changes in survival rates for long-lived wader species.
  • Cannon-netting Oystercatchers is not easy! The lack of consistent annual catching success and biases associated with, for instance, just catching the edge of a flock (where juveniles tend to be concentrated), are probably reflected in the fact that no recruitment patterns could be established.
  • WeBS Core Count data showed a significant long-term decrease in the population of Oystercatchers wintering in the Burry Inlet and a long-term increase in the population in Carmarthen Bay. During the period 1997 to 2017 there was a correlation of the two sets of figures – as Burry numbers declined, Carmarthen went up and vice versa (see figure below). Counts of Oystercatcher in the Burry Inlet were weakly associated with cockle biomass in the estuary. Carmarthen Bay counts were more strongly linked to Burry Inlet cockle biomass, increasing as cockle supplies dropped in the Inlet.

Take-home messages

In the study by Katharine Bowgen and colleagues, an apparently underexploited area within the Carmarthen Bay SAC became a vital resource when food supplies collapsed in the Oystercatchers’ preferred feeding area.

Understanding how birds can (and may need to) respond to changing food resources is important, given ongoing pressures from shell-fishers and the fact that the distribution of invertebrate prey stocks may be affected by climate change. The ongoing cockle decline in the Burry Inlet is of concern to both the fishermen, reliant on the stocks, and to conservation managers monitoring bird populations. This study suggests that Oystercatchers may be able to adapt during periods of stress but only if alternative foraging areas are available in the local vicinity.

The analysis of long-term datasets allows more accurate understanding of incidents such as the cockle crash investigated here and improves our abilities to manage their effects on longer-lived species such as waders. Only through long-term monitoring is it possible to fully understand the consequences of major changes in species’ resources and how individuals might adapt to cope with their impacts.

Population level effects

The following three WaderTales blogs contain information about how wintering conditions in particular study areas can affect wader populations.

Sanderling migration

In A place to roost, there is a section about the consequences for local Redshank when Cardiff Bay was permanently flooded, with links to three important papers. Birds that moved elsewhere had difficulty in maintaining their body condition in the winter following removal of their feeding habitat and continued to exhibit lowered survival rates in subsequent years.

In Travel advice for Sanderling,there is clear evidence that poor wintering conditions affect survival rates, the probability of breeding in the first summer and the timing of spring arrival in Greenland. All of these three factors can have population-level effects for the species.

In Gap year for sandpipers, we learn that Semipalmated Sandpipers may not breed every year, depending upon the condition they are in when it is time to migrate.

These three stories are all relevant to the Burry situation. Oystercatchers that were in poor condition at the end of a winter, either because they stayed in the Inlet and had fewer resources or because they moved to new sites, may not have had the resources to migrate to their breeding areas in some years or could have migrated later, either of which may reduce the number of potential breeding attempts within a season (see Time to nest again?).

Conservation implications

Although the analyses presented here were undertaken in order to understand what happened in the Burry Inlet, a site designated in part because of the high Oystercatcher counts, the authors emphasise just how important networks of sites are to wider shorebird conservation issues, especially if there is a rapid change in the quality of a core area. It is not sufficient just to protect the very best sites.

This paper could not have been written without the work of volunteer counters and ringers

With coastal wader populations exhibiting long-term declines globally, understanding how they respond to changes in their prey is important, especially given the potential for warming seas to affect invertebrate populations. In this context, the Burry Inlet study demonstrates the value of long-term WeBS counts and the efforts of local ringers. The contribution of volunteers is warmly acknowledged at the end of the paper.

Resilient protected area network enables species adaptation that mitigates the impact of a crash in food supply. Bowgen, K.M., Wright, L.J., Calbrade, N.A., Coker, D., Dodd, S.G., Hainsworth, I., Howells, R.J., Hughes, D.S., Jenks, P., Murphy, M.D., Sanderson, W.G., Taylor, R.C. and Burton, N.H.K. MEPS. DOI:https://doi.org/10.3354/meps13922


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.

Who eats African Oystercatcher eggs?

As ornithologists, focused as we are upon birds, we perhaps find it hard to fully acknowledge birds’ eggs as key ‘consumables’ in the food web – a ready source of protein for everything from snakes to deer.

Nest cameras have shown that clutches of ground-nesting waders are taken opportunistically, by grazing sheep for instance, but there are also some species – or individuals – that are specialist egg hunters. See Prickly problems for breeding waders (hedgehogs) and Curlews and foxes in East Anglia (sheep).

In their paper in Wader Study, Itxaso Quintana, Rio Button & Les Underhill describe a single-year study of the predation of African Oystercatcher nests on Robben Island, best known for the prison where Nelson Mandela was held for eighteen years, and for its important seabird colonies. Introductions and eradications on Robben Island have created a far-from-natural food-web that is ever-changing. The situation that Itxaso, Rio and Les found in the 2019/20 breeding season included Kelp Gulls ‘protecting’ African Oystercatcher nests from the attentions of Mole Snakes – something that makes little sense unless set in a historical context, as the authors do in their paper.

What a mess!

Homo sapiens has interfered spectacularly on Robben Island, in the same way as in so many other places, with exploitation of seals, the introduction of an array of large mammal species from the mainland during the apartheid era, and the introduction of rabbits, fallow deer and cats. By 2019/20, the rabbits and almost all of the deer had been removed, encouraging the regeneration of ground cover, and over 90% of the cats had been culled. The remaining threats for African Oystercatcher nests were expected to come mostly from Kelp Gulls, native Mole Snakes and the small number of remaining cats.

Checking out an Oystercatcher’s nest on the shoreline

The 550 African Oystercatchers on Robben Island account for 8% of the species’ population, making this a very important breeding site. This total comprises both nesting pairs and non-breeding birds. African Oystercatchers do not migrate, relying on local shellfish supplies year-round. In 2000, the species was classified as ‘near threatened’ but, thanks to the spread of the invasive Mediterranean Mussel along the South African coast, numbers have recovered. Native shellfish might be in trouble but at least the African Oystercatcher can now be considered to be of ‘least concern’!

The 2019-20 breeding season

Robben island has a coastline which is less than 10 km in length, enabling the authors to monitor 158 nesting attempts of what is thought to have been 133 pairs of African Oystercatchers. A further 300 non-breeding oystercatchers were also present. There were three main study sections, corresponding to the north end of the island (63 nests), the south end of the island (64 nests) and the east side (29 nests). The nest success rates of nests in the north and south were very different, with rates in the east being intermediate.

Below the gull colony in the north of the island, 45 out of 63 African Oystercatcher nests were successful (71%) with one failure associated with Mole Snakes.

Away from the gull colony, in the south of the island, only 14 out of 64 African Oystercatcher nests were successful (22%) with 17 failures associated with Mole Snakes and the reason for most failures unknown.

Breeding Kelp Gulls are spreading across the northern part of Robben Island

There was far more evidence of Mole Snake activity in the south of the island, as can be seen in the map, with individual snakes seemingly ‘patrolling the shoreline just above the spring high tide level, where African Oystercatchers lay their eggs’. In the north, where African Oystercatchers nest on the shoreline immediately below the Kelp Gull colony, snakes were much less conspicuous. You can read more about this in the paper.

Two decades of research

The long-term study of African Oystercatchers on Robben Island started in 2001. Since then, the population has increased fourfold and the number of nests has almost doubled. There have been many changes over this period, as you can read in the paper, but the most significant one for African Oystercatchers is the arrival of Mediterranean Mussels, first noticed in South African waters in 1979 and already colonising the shoreline of Robben Island by 2003. These invasive mussels provide more food than native shellfish and the authors suggest that this has fed through into higher oystercatcher nesting densities.

The beak of an African Penguin is enough to deter Mole Snakes

Over the two decades, there has been a massive change in the populations of potential predators. In the early part of the research period, Mole Snakes were considered relatively unimportant, in terms of predation pressure on African Oystercatchers. Introduced cats, however, then became a major problem, with numbers growing between 2001 and 2005, to such an extent that at least 83% of African Oystercatcher nests were predated in the 2004/05 breeding season. Culls in 2005 and 2006, followed by continued controls, have lowered cat numbers to fewer than ten individuals.

There were no Kelp Gulls breeding on Robben Island until 2000/01, when the first five nests were found. More and more birds now make the short commute to Cape Town, to scavenge, and 2829 gull nests were recorded in 2019/20. Like other large Larus gulls, Kelp Gulls have a reputation as egg thieves. However, on Robben Island, where there are few people disturbing nesting African Oystercatchers, and forcing them to leave their nests, the gulls seem to cause few problems. Instead of being a threat, Kelp Gulls attack Mole Snakes, thereby protecting the eggs of the African Oystercatchers.

For Kelp Gulls, it’s only a short commute to Cape Town, where they scavenge for food

Four other species have benefited from reduced cat numbers. As hoped, numbers of Hartlaub’s Gulls and Swift Terns have both increased, while Mole Snakes have experienced higher survival because the eggs of these two species are available in the austral autumn and winter. African Penguins have benefited too, as a consequence of reduced cat predation, and their sharp beaks can deal with Mole Snakes.

What next?

Hatched Oystercatcher chick and another one on the way

The current situation seems to suit all of the species considered here. Removing introduced herbivores has provided more suitable habitat for snakes, and nesting numbers of key seabirds and African Oystercatchers have all increased since most cats were culled.

Robben Island is not a natural ecological system, however. Major perturbations have happened over decades, with introductions, extirpations, culls and the arrival of invasive species. For the moment. the authors see no reason for Kelp Gulls and/or Mole Snakes to be controlled, in order to support African Oystercatcher numbers or protect important seabird populations.

Cold searching the area above the tide-line to locate nests of African Oystercatchers (Mole Snakes do the same)

One thing that seems almost certain is that the situation will change again: the local Mediterranean Mussel population could collapse, for example due to disease; a pollution incident in the busy sea lanes into the port of Cape Town could suddenly impact birds and/or their food supplies; the grinding effects of climate change, particularly the risk of increased storminess, could slowly upset the equilibrium; diseases such as avian influenza, currently affecting Cape Cormorants, could spread further; or the cat population could explode again. Robben Island looks like a fascinating place in which to study complicated predator-prey interactions; here’s hoping that long-term monitoring will continue.

Paper

The full paper is available in Wader Study, the journal of the International Wader Study Group.

African Oystercatchers on Robben Island, South Africa: The 2019/2020 breeding season in its two decadal context.
Itxaso Quintana, Rio Button & Les G. Underhill. Wader Study.


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.

More Curlew chicks needed

There are three ways to increase the number of Eurasian Curlew in the UK; boost chick production across the breeding range, find ways to ensure more chicks recruit to the breeding population and/or maximise the lifespan of breeding birds. In a paper in Biological Conservation, Aonghais Cook and colleagues show that, while continued protection of wintering sites is really important, there appears to be little scope for conservation action that can further increase annual survival rates. The focus for conservationists has to be on increasing chick productivity and recruitment.

Curlew in Britain and Ireland

The once-common breeding Curlew is becoming harder to find in many areas. We know that productivity is generally low but could reduced annual survival rates also be contributing to the speed of disappearance? Here’s a quick summary of the story so far.

  • The Eurasian Curlew is designated as ‘near threatened’, as discussed in this WaderTales blog.
  • A 2017 paper by Sam Franks and BTO/RSPB colleagues described the main factors associated with the species’ decline in Great Britain. This work is summarised in a WaderTales blog called Curlews can’t wait for a treatment plan.
  • Estimated breeding population declines since 1995 are 69% in Wales, 59% in Scotland and 31% in England (Breeding Bird Survey). This is not as bad as in Ireland, where 96% were lost between the 1980s and 2015-2017. See Ireland’s Curlew Crisis.
  • Huge numbers of Curlew cross the North Sea at the end of the summer, particularly from Finland. Recent population estimates show that British wintering numbers dropped by 14% in just eight years, with an Irish decline of 13% in five years. See two reviews of wader population estimates, based upon waterbirds papers in British Birds and Irish Birds.

Survival of adult Curlews

As discussed in Measuring shorebird survival, a change in adult survival rates can have a huge effect on shorebird populations. If a species’ annual survival rate drops from 90% to 80% then numbers can half in just six years. We have seen these sorts of dramatic declines in populations of waders that travel between Russia/Alaska and Australia. There’s more about this in Wader declines in the shrinking Yellow Sea.

There are several factors that could be affecting survival rates of British-wintering Curlew:

  • Warmer winters might be expected to lead to increased survival rates.
  • The shooting ban, introduced in 1982 in response to declining Curlew numbers, was specifically designed to increase survival rates.
  • As local wintering populations have dropped, competition for resources could have dropped, potentially leading to increased survival rates.

In their paper about survival rates of Curlew in North Wales, published in Bird Study in 2013, Rachel Taylor and Steve Dodd detected an increase in apparent survival from 86.9% to 90.5% that coincided with the cessation of hunting. They also found that mechanical cockle harvesting in the mid-1990s occurred at the same time as a reduction in apparent survival rate of Curlew from 95% to 81%, indicating the potential for management changes to have huge, unintended consequences for wintering Curlew.

Amassing the data

The research team analysed recoveries of Curlew marked as chicks and adults in the breeding and winter periods, in order to estimate annual survival and the proportion of birds available to recruit into the breeding population.

Thanks to the efforts of skilled, volunteer ringers, two large data-sets were available, collected during the period 1970 to 2018:

  • A total of 1293 adult birds, 144 juveniles and 14,277 chicks were ringed in their breeding grounds across Great Britain.
  • During the winter period, 4403 Curlew were caught and ringed in five key sites – the Severn Estuary, the Tees Estuary, the Wash, Traeth Lavan and the Moray Firth (see map). Supplementary colour-ring sightings were available for the Wash, Tees and Severn.

Full details of how data were used and how models were developed are provided in the paper.

How well do Curlew survive?

Analysis of breeding season data for the period 1970 to 2018 indicates that the average annual survival was 89.8% (confidence interval 0.871–0.920) for adults and 32.6% (0.278–0.378) for first-years. The period of steepest population decline, between 1983 to 1991, coincided with lower survival in both age classes. Encouragingly, since 1996, survival has increased to 92.2% (0.886–0.948) for adults and 39.0% (0.304–0.484) for first-years.

The British and Irish wintering population of Curlew is drawn from a vast area, with birds arriving from as far as Russia and lots of birds from Finland. In a recent breeding wader report covering the Fennoscandia region, no overall change in Curlew numbers was detected, with declines in Norway and Sweden balanced by increases in Finland (see Fennoscandian Wader Factory). From 1970 to 2018, survival rates of UK wintering Curlew averaged 88.4% (0.875–0.893), consistent with survival rates of the British breeding population (above).

Survival varied over time and between the five study sites but has been generally greater than 90% in recent years. Increases in survival were recorded on the Severn Estuary and The Wash.

Curlew struggle in winters with large number of frost-days and survival rates drop significantly, both in that winter and over the subsequent year

Survival was lower in winters with a greater number of days of air frost, an effect exacerbated in successive cold winters. Cold weather may have contributed to low survival in the 1980s, a pattern also evident in the analysis of breeding season data.

Resources may limit numbers. The study suggests that, for four out of five sites, survival was lower in years in which the number of Curlew on a site was higher.

Nationally, the research team found no strong evidence that the hunting ban had increased survival rates. However, there appeared to be local effects on The Severn Estuary and on the Wash. It is unfortunate that national bag data are not available to indicate whether Curlew hunting was particularly prevalent in these two estuaries in the period prior to 1982.

What does this all mean for Curlew conservation?

Birdwatchers are helping to monitor annual survival rates by reporting sightings of colour-marked birds

Since 1996, the mean annual adult survival rate of the British Curlew breeding population has been about 92%. Despite this high number, the Breeding Bird Survey tell us that there has been an observed decline in breeding numbers of 3% per year. Demographic modelling suggests that four breeding pairs must be producing an average of only one chick per year between them. This low figure may come as no surprise to Curlew fans.

To achieve sustainability, the authors conclude that the current figure of 0.25 chicks per pair needs to rise to 0.43 chicks per pair. There are estimated to be 58,000 pairs of Curlew in Great Britain (paper in British Birds). Currently they might be producing about 14,500 chicks each year, on average, and they need to produce nearly 25,000 chicks. British Curlew need to fledge 10,000 more youngsters – every year – just to arrest the decline in numbers.

Personal reflections

Currently, annual survival rates of adults are consistently high but a couple of cold winters, changes to shellfish policy, tidal barrage developments, inappropriately-sited wind turbines and unrestricted disturbance could all have serious negative effects. It is important that we continue to protect the UK’s estuaries and the grassland feeding and roost sites that fall outside their boundaries.

Many Curlew spend significant amounts of time on farmland and recreational land that is not protected in the same way as estuarine habitats

There are a couple of gaps in our knowledge about Curlew demography. When do Curlews first breed and what are survival rates during the ‘teenage’ pre-breeding years? A working hypothesis would be that most breed at age two, with possibly some earlier and probably some later. More colour-ringing of chicks will hopefully provide better data on recruitment age and teenage survival rates. This issue was discussed in Teenage waders. In the meantime, perhaps more thought needs to be applied to avoiding disturbance of non-breeding flocks during the summer holiday season?

It is going to be important to understand how quickly juveniles recruit to breeding populations

It almost goes without saying – Curlews need to produce more chicks. Local conservation initiatives, whether by tenant farmers or dukes with vast estates, will help but raising 10,000 more chicks per year will likely require changes in land management policies. Can agri-environment initiatives be refined to deliver more Curlew? How do we integrate tree-planting and upland conservation priorities? Where should wind turbines be sited? And so much more!

Paper

In their summary of their paper, Aonghais Cook et al concluded that “In addition to increasing productivity, effective conservation strategies will need to maintain high levels of survival, which requires an improved understanding of population connectivity and demographic variation throughout the annual cycle.”

The full paper can be read here:

Temperature and density influence survival in a rapidly declining migratory shorebird.

Aonghais Cook, Niall Burton, Stephen Dodd, Simon Foster, Robert Pell, Robin Ward, Lucy Wright & Robert Robinson. Biological Conservation


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.

Oystercatcher Migration: the Dad Effect

What determines whether some birds migrate and others do not? This question is fundamental to understanding how migratory systems change over time but the causes of individual migratory behaviours have proved difficult to isolate.

Verónica Méndez and colleagues are studying Icelandic Oystercatchers, some of which remain in Iceland for the winter but most of which migrate across the Atlantic to Ireland, Britain and mainland Europe. In a 2021 paper in Scientific Reports they show that a chick’s migratory behaviour seems to align with the behaviour of its father but not its mother. What can explain this pattern?

The story so far

The Icelandic Oystercatcher study system has already featured in three WaderTales blogs. The first was Migratory decisions for Icelandic Oystercatchers. This focused upon the key questions that Verónica Méndez and colleagues from the universities of Iceland, East Anglia (UK) and Aveiro (Portugal) are trying to answer.

  • Why do some Oystercatchers migrate when others don’t?
  • Is it the same birds each year?
  • Do resident or migrant birds have an advantage when it comes to choosing a territory and raising chicks?
  • Do chicks follow the same migratory patterns as their parents?

When the first blog was written, in 2015, eight colour-ringed Oystercatchers had been seen in Ireland and the UK, and five had been seen wintering in Iceland. Fast forward to the next blog in 2018 – Mission impossible? Counting Iceland’s wintering Oystercatchers – where counts showed that over 11,000 Oystercatchers spend the winter in Iceland. Using colour-ring sightings of resident and migratory birds, the research team concluded that this total is about 30% of the whole Icelandic population. The other 70% fly south across the Atlantic each autumn, with no individuals yet observed to change what they do between years.

In the third blog – Which Icelandic Oystercatchers cross the Atlantic? – some patterns were starting to emerge.

  • Females and males are equally likely to migrate.
  • Size does not matter – small and big birds are equally likely to migrate
  • There are regional patterns across Iceland, with birds breeding in the west being most likely to be resident.
  • Birds do not pair up assortatively – residents don’t pair up with other residents before the migrants return, for instance.

Family ties

In most species of waders, parents protect their chicks and take them to suitable feeding areas but they do not actively feed them. Parental care in European Oystercatcher includes foraging for food and bringing it back to the chicks. This is why it is possible for Oystercatchers to nest on the roofs of buildings (Oystercatchers: from shingle beach to roof-top), where they are out of the reach of ground predators.

Focusing on chicks

To be able to understand the relationship between migratory behaviour in adults and their chicks, you need to be able to mark and then attempt to follow all of the members of a family. Adult Oystercatchers generally keep the same mates and nest in the same areas year after year, enabling the establishment of marked population of birds in different parts of Iceland. Between 2015 and 2018, a total of 615 incubating adults were caught. By following the outcomes of nesting attempts and then monitoring the growth of chicks, the research team also managed to individually mark 377 chicks.

Three colour-ringed chicks. Where will they go?

The success of the whole project relied heavily upon winter sightings of marked birds within Iceland and in Ireland, the UK and continental Europe. Through a network of volunteer observers reporting sightings of marked individuals across the wintering range, the migratory behaviours of 227 of the 615 colour-marked adults and 50 of the 377 colour-marked chicks had been identified at the time that this paper was written. In addition, it was possible to infer the migratory behaviour of 353 marked adults using measurement of isotope ratios (δ13C and δ15N) of feathers that were grown in the winter (as described here).

The analyses in the paper by Verónica Méndez and her colleagues are based upon 42 marked chicks of parents for which the migratory behaviour of both parents is either known or can be inferred from isotopic signatures. These chicks all fledged successfully and were seen during the winter period, either in Iceland or having crossed the Atlantic. In three cases, two chicks from the same broods are known to have behaved in the same way. More data have become available since the analyses, all confirming the same patterns.

Results

It is possible to imagine a scenario in which late or slow-growing Oystercatcher chicks might be more likely to stay in Iceland than their more mature counterparts – simply by developing too late to gain enough resources to cross the Atlantic. Analysis of hatch dates and growth parameters did not suggest the existence of such a link, as described in the paper.

This young Oystercatcher was spending its first winter on the coast of western Iceland

The interesting finding of this study is the link between the behaviour of parents and chicks. Data generated by observations of colour ringed individuals (adult and chicks) and from isotopes (adults) established 21 chick/parent associations.

  • Of the sixteen chicks raised by migrant mothers, eight migrated and eight remained in Iceland.
  • Of the five chicks raised by resident mothers, three migrated and two remained in Iceland.
  • All ten of the chicks raised by migrant fathers migrated from Iceland.
  • Of the eleven chicks raised by resident fathers, one migrated and ten remained in Iceland.
  • Seven chicks that fledged from pairs with one resident and one migrant parent adopted the migratory behaviour of the father.

This is pretty compelling evidence that chick migratory behaviour is associated with paternal (and not maternal) migratory behaviour!

What does this mean?

There is no evidence of genetic control of migratory destinations and both Oystercatcher parents care for chicks, so what mechanism could produce such strong paternal but not maternal effects?

The authors suggest that the migratory behaviour of individual oystercatchers may be linked to social interactions they experience during the post-fledging period. In shorebird species, such as Oystercatchers, mothers commonly depart before the chicks fledge, or at about the same time. Fathers often provide parental care for longer and this extended period of the parental bond may underlie the link between paternal and juvenile migratory behaviour in Icelandic Oystercatchers. Despite being able to fly and feed independently, juvenile Oystercatchers in Iceland have been seen begging for food several months after fledging, suggesting that some parents (most likely fathers) may care for youngsters much longer than in other species.

This Iceland-ringed Oysterctatcher was photographed in Guernsey in January 2021. It departs at the start of February each year.

Under this extended-care system, a chick that is being look after by a resident male may well become a resident, simply by following dad. As autumn arrives, the youngster can follow his parent when he moves to the coastal mudflats where resident Icelandic Oystercatchers spend the non-breeding season. Autumn turns to winter and the chick is destined to be a resident.

Is it possible to explain a similar link for migrants? As the breeding season comes to an end, migrant fathers leave their breeding areas and head south, across the Atlantic, leaving fledged youngsters to fend for themselves. Groups of youngsters gather together in flocks which also include adults that are feeding up in preparation for migration. Although not influenced by their own fathers, chicks may follow the cues of other migratory adults, thereby creating the patterns seen in this paper.

Most of the chicks included in these analyses were early-fledged birds, simply because earlier nesting attempts tend to be more successful. The research team were unable to detect any significant effect of fledging date on migratory behaviour but they do not rule out the possibility that late-fledging individuals lack the time or resources to undertake a migratory journey, irrespective of paternal behaviour.

The broader context

Migratory behaviour typically arises in seasonal environments, allowing individuals to exploit peaks of resource abundance in distinct locations across the world. Rapid shifts in the distribution and migration phenology of many migratory species present challenges to site-based conservation strategies. There is an urgent need to understand the processes that influence individual migratory behaviour, in order to attempt to predict species’ responses to environmental change.

The findings in this paper suggest that the social interactions experienced by individuals can directly influence the development of their migratory behaviour, and that the extent and timing of parental care may be key in shaping individual access to these social interactions. You can read the full paper here:

Paternal effects in the initiation of migratory behaviour in birds Méndez V., Gill, J.A., Þórisson, B., Vignisson, S.R., Gunnarsson, T.G. & Alves J.A.


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.

Cycling for waders

This blog is mostly about Black-tailed Godwits but there’s stuff about cycling too!

If you’re a Black-tailed Godwit, a 2800-mile (4500-km) direct flight from East Anglia to West Africa is estimated to burn 1085 Calories (4500 kJ) of energy (Alves & Lourenço). Fuelled by Cambridgeshire worms, a female godwit that was raised by the Project Godwit head-starting team flew from the Nene Washes to wetlands in south-east Mauritania in just two days. ‘Cornelia’ – as she was named – undertook this marathon journey with no pre-season training. She just took off on 13th August and arrived on the 15th.

To raise money for Project Godwit and for research projects funded by the International Wader Study Group, Jen and Mark Smart cycled from Somerset to East Anglia, on a 600 mile (960 km) journey that links sites that have been visited by head-started Black-tailed Godwit chicks. Each of them burnt 15,000 Calories (62,800 kJ) over the course of eight days, taking in high energy foods as they travel and stopping to feed and rest each night. Unlike Cornelia, Mark and Jen had been training for years.

Quick reminder of head-starting

Black-tailed Godwits breeding in East Anglia face huge challenges, as you can read below. Four years ago, their situation had become so perilous that it was decided that the only way to stop them disappearing completely was to hatch eggs in incubators and raise chicks in captivity. You can read more about head-starting here. Project Godwit is a partnership between RSPB and WWT, with major funding from the EU LIFE Nature Programme, the HSBC 150th Anniversary Fund, Natural England, the National Lottery Heritage Fund through the Back from the Brink Programme, Leica and the Montague-Panton Animal Welfare Trust.

The maps below show the two breeding sites (Ouse and Nene Washes) and all the late-summer passage sites where head-started birds have been seen in England (left), and the international sightings of all godwits ringed in these breeding sites.

International Wader Study Group (IWSG)

The International Wader Study Group brings together everyone who has a passion for waders (shorebirds), the habitats they use and their conservation. Members include research scientists, citizen scientists and conservation practitioners from all around the world. IWSG gives out small grants each year that help to support wader projects around the world. Recent grants have been used to discover the wintering areas of Common Sandpipers, to measure the site-faithfulness of Dotterel and to support projects in Azerbaijan, Albania, Bangladesh & Argentina.

Mark and Jen

Jen Smart has worked for the RSPB for 14 years.  As a scientist, she led RSPB’s research into the conservation problems faced by breeding waders and developed solutions to help these species. See the WaderTales blog Tool-kit for wader conservation. She developed the science programme around Project Godwit and maintains a keen interest in the project. Jen is Chair of the International Wader Study Group.

‘Manea’ arrived at Old Hall Marshes (Kent) with his sister, ‘Lady’, in July 2017

Mark has worked for the RSPB for 26 years and is Senior Site Manager at Berney Marshes, a 600 ha grassland nature reserve with around 300 pairs of breeding waders. See the WaderTales blog Managing water for waders. As well as managing the reserve, Mark works with other land managers across the country to develop and implement ways of improving habitats for breeding waders.

Latest news from Project Godwit

Project Godwit has been trialling the use of head-starting (https://projectgodwit.org.uk/), where young godwits are reared in captivity, safe from predators and potential flooding, and released once fledged. The aim is to boost the number of godwits breeding in England. The cycle route for Mark and Jen links eleven nature reserves in England, managed by a range of conservation organisations, where head-started Black-tailed Godwits have been spotted on migration by local birdwatchers.

Nelson is one of the birds carrying a geolocator but he has not been recaught (yet)

The ride started at WWT Steart Marshes in Somerset; visited by a Black-tailed Godwit named ‘Nelson’ in 2017. Birdwatchers throughout England were put on alert when the first head-started Black-tailed Godwits were released in 2017 but it was a surprise when Nelson headed southwest. Nelson is a star of Project Godwit. He returned to the Ouse Washes in 2018 and paired up with another head-started bird called ‘Lady’. They have met up in each subsequent spring. In February, Nelson spends time on the Tagus Estuary in Portugal but we don’t know whether he is one of the limosa Black-tailed Godwits that winters south of the Sahara.

The map below shows the route taken by Mark and Jen. The original plan was to cycle from Norfolk to the IWSG conference in Germany, which neatly linked the two causes for which they are seeking sponsorship – Project Godwit and the IWSG fund to support wader research. When the conference was rescheduled as an on-line meeting, they decided to join up the godwit dots across England. The 600-mile bike took just over a week.

Jen & Mark’s route links RSPB, WWT, Wildlife Trustand county wildlife sites between Somerset and Cambridgeshire.

The last site to be visited was the Nene Washes where, as mentioned above, the Black-tailed Godwit ‘Cornelia’ returned to breed. Having been raised at Welney, she was released at the Nene Washes on 27 June, 2018, wearing a small geolocator attached to a flag on her lime ring (see earlier picture). She is the only bird for which the RSPB and WWT team have a whole-year migration history. Cornelia was caught on a nest at the Nene Washes in 2019 and her geolocator was removed. In his blog on the Back from the Brink website, Mo Verhoeven shares his excitement when he learned that this young bird had flown directly from the Nene Washes to wetlands in Mauritania in just two days. There is more about Cornelia here.

Conservation challenges

Wetlands are under threat across the globe and it is appropriate that Mark and Jen are raising money for the International Wader Study Group and for Project Godwit. As they tweeted about their travels and talked about Black-tailed Godwits at local press events, at different nature reserves, they revealed some of the conservation challenges that waders face.

The RSPB nature reserve at Titchwell (North Norfolk) is a favourite pit-stop for Project Godwit birds. These three youngsters, all head-started in 2018, visited before flying south.

Project Godwit is not just about head-starting more Black-tailed Godwit chicks. The team is trying to improve the chances for nesting birds out on the Washes, using electric fences and other predation reduction schemes, and through the development of alternative breeding areas that are under less threat of flooding during spring and summer deluges.

Within Britain and when they head south through Europe and into Africa, Black-tailed Godwits are dependent upon a network of sites. Some of them are fully-protected nature reserves, others have been given international recognition as SPAs and Ramsar sites, but there are many other locations that are important but not designated. Sightings of Project Godwit birds and locations downloaded from geolocators will help to identify areas in which birds may be vulnerable to habitat change and new developments.

A new airport that is planned for the Tagus Estuary is a huge threat to limosa Black-tailed Godwits that breed in Western Europe, including the small English population. It’s thought that about half of the Project Godwit birds use the rice fields and mudflats of the Tagus Estuary, as you can read in Black-tailed Godwits are on their way home. As mentioned above, Nelson has been seen in the Tagus Estuary on several occasions (see map alongside). The proposed airport threatens many species of migrant waterbirds (Tagus Estuary: for birds or planes).

An important unknown when trying to conserve our larger wader species is ‘what happens to the teenagers?’. When do species such as Black-tailed Godwits start to breed and what do they do in the period between fledging and breeding? A key part of Project Godwit is to mark chicks in the wild, as well as head-started birds, hopefully answering questions such as ‘what proportion breed in their first year?’ and ‘where do immature birds spend the pre-breeding years’? Perhaps the International wader Study Group will be able to support similar work for other large shorebird species, through its small project grants?

Support for Mark and Jen

This epic sponsored cycle ride is funding work by Project Godwit and the IWSG. It was a great opportunity to thank colour-ring readers who have reported marked birds, to emphasise the importance of protecting networks of sites for migrant waders, and to highlight some of the conservation challenges that lie ahead.

If you would like to help Mark and Jen to support International Wader Study Group Small Projects Grants, please donate here: https://www.waderstudygroup.org/donate/

If you would like to help Mark and Jen to support the RSPB’s contribution to Project Godwit please donate here: https://www.justgiving.com/fundraising/fundsforwaders


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.

Is the Curlew really ‘near-threatened’?

If a Curlew can live for over 32 years and there are flocks of 1000 in Norfolk, how can they be described as near-threatened? 

Dark times lie ahead for Curlew? (© Graham Catley)

Dark times lie ahead for Curlew? (© Graham Catley)

Dec 2021 BT Curlew changedThirty years ago there were eight members of the world-wide curlew family but now we may well be down to six.  The planet has lost one species, the Eskimo Curlew, with no verified sightings since the 1980s, and probably the Slender-billed Curlew as well.  Of the others, Far Eastern Curlew and Bristle-thighed Curlew are deemed to be endangered and vulnerable**, respectively, and our own Curlews are classed as near-threatened, which is the next level of concern. This may seem strange, especially when flocks of 1000 can be seen on the Norfolk coast.  However, evidence suggests that we should take heed of what is happening to other members of the curlew family, as we consider the future of this evocative species with its wonderful bubbling curl-ew calls.

** Bristle-thighed Curlew has now been changed to ‘near-threatened’. Graphic alongside has been changed.

Our Curlew – more properly called the Eurasian Curlew – was until relatively recently a locally popular game species in Britain, especially in September and October, when birds are reputed to be particularly flavoursome.  A male Curlew is equivalent in weight to a Wigeon (or two Teal) and the bigger female may well be as heavy as a Mallard, so it is not surprising that they were worth targeting.  They came off the British quarry list in 1981.

Map showing movements of ringed curlews. Purple dots indicate where British/Irish ringed birds have been recovered and orange dots show ringing sites of birds found here and wearing foreign rings. Maps of movements can be found on the BTO website at http://www.bto.org/volunteer-surveys/ringing/publications/online-ringing-reports

Purple dots indicate where British/Irish ringed Curlews have been recovered and orange dots show ringing sites of birds found here and wearing foreign rings. Maps of movements can be found at http://www.bto.org/volunteer-surveys/ringing/publications/online-ringing-reports

The Curlews that we see on the Norfolk coast in autumn and winter are drawn from a wide breeding area; some are of British origin but many are from Scandinavia, Finland and Russia.  The Wash Wader Ringing Group recently received a report of a bird that was ringed in Norfolk in September 2000 and recovered in Izhma in Russia in May 2014.  At 3300 km (2000 miles) this is nearly as far away as the furthest east dot on the map of Curlew recoveries, shown here and published on the website of the British Trust for Ornithology.  The bird was an adult when ringed so must have been at least 15 years old when shot.  This seems like a good age for a Curlew but is less than half of the British longevity record, set by a chick ringed in Lancashire in 1978 and found dead on the Wirral in 2011.

Curlew mortality is higher in severe winters (© Graham Catley)

Curlew mortality is higher in severe winters (© Graham Catley)

Curlew numbers on the Wash, which sits between the counties of Norfolk and Lincolnshire, increased dramatically when shooting ceased in 1981, although milder winters could have also have been influential.  In the five years immediately before the ban, the average maximum, winter Wetland Bird Survey count on the Wash was 3281, rising to 9642 in the period 2006/07 to 2010/11.  There were similar increases on the North Norfolk coast and a bit further south at Breydon Water.  The broader, national picture is one of increase between 1981 and 2001, although generally at a lower level to that seen in Norfolk, followed by a steady, shallow decline.  If numbers are higher than they once were does this mean that we should be less concerned about Curlews – and what is the justification of the species’ near-threatened designation?

Curlews fly vast distances to spend the winter on the estuaries of Britain & Ireland (© Graham Catley)

Curlews fly vast distances to spend the winter on the estuaries of Britain & Ireland (© Graham Catley)

Conserving migratory species is difficult because individuals rely on different resources in different countries at different stages of the year.  For Curlews, there is evidence that breeding season problems are at the heart of large decreases in numbers in Russia, through the Baltic and into The Netherlands – the countries from which much of the wintering population on the east coast is drawn.  According to the European Commission’s species management plan, drivers of decline include wide-scale intensification of grassland management for milk production, land-abandonment and increased predation in some areas.  Autumn, winter and spring hunting is thought to have had a lesser but contributory effect to the long-term losses, with hunters across the European Community shooting between 3% and 4% of the population each year.  In the last twenty years, within the EC, hunting of Curlew has been confined to Ireland, Northern Ireland and France.  Much of this shooting pressure was and in France, where coastal hunting of Curlew was reinstated after a five year moratorium but has since been suspended again. Read blog about this here.

curlew webpageFocusing on Britain and Ireland, we have seen major losses in our breeding populations.  In Ireland, the Curlew population is estimated to have dropped from 5000 to 200 pairs in the twenty years between 1991 and 2011 (with further declines since – see Ireland’s Curlew Crisis blog below). There has been an 80% decline in Wales and other losses elsewhere.  There’s more about these distributional changes in a 2012 article written for the BTO website.

Curlew productivity in several areas appears to be very low and it is possible that the adults we are seeing are part of an ageing population.  As has been shown in seabirds, counts of adults can give a false sense of security, as it is easy not to notice that there is little recruitment of new, breeding adults into the population, with obvious long-term consequences.

Graph shows the changing Curlew population in Great Britain (Wetland Bird Survey)

Graph shows the changing Curlew population in Great Britain (Wetland Bird Survey)

The decline in the number of breeding Curlew in Great Britain is clearly reflected in monthly, winter counts undertaken by volunteers on west coast estuaries.  On the Dee, for instance, the average peak-winter count dropped from 6109 in the early 1970s to 4348 in the five years after the shooting ban, rose to 5081 in the late 1990s but then slipped back to 3802.

In Ireland and Northern Ireland, a total ban on shooting Curlew was announced in 2012, brought in once it was clear that the estimated November harvest of between 6% and 8% was unsustainable and set against a background of the collapse of the local breeding populations.  The same local reasoning lies behind continuing protection in Wales, western England and in much of Scotland, especially at a time when financial support to land-managers is being used to try to bolster British breeding numbers.  In eastern England, Curlew conservation has a more international flavour, as we provide a safe haven for birds from as far away as Russia.

With relatively few continental birds, the Wetland Bird Survey trend reflects more local declines

With relatively few continental birds in Northern Ireland, the Wetland Bird Survey trends probably reflect local declines

Britain & Ireland, between them, provide winter homes for half of the Europe-wide population of Curlews (about 210,000 out of 420,000), with the Netherlands holding 140,000 birds.  There are also significant flocks in Germany and about 20,000 in France.  These may seem like reasonable numbers but, given that fewer chicks are being raised, the number of adults is declining, two close relatives have been driven to extinction and other curlew species are in trouble, the label of near-threatened seems highly appropriate.

We should be proud of our wintering Curlews in Great Britain, where numbers have stabilised, albeit at a level that is 20% lower than at the turn of the century, but there is no room for complacency in Northern Ireland, where the decline continues.

Update: Curlew was added to the red list of the UK’s Birds of Conservation Concern on 3 December 2015

Other WaderTales blogs about Curlew

  • Why are we losing our large waders? takes a look at a review of the common threats faced by the 13 Numeniini species (godwits, curlews and Upland Sandpiper).
  • Curlews can’t wait for a treatment plan focuses on the primary drivers of the species’ breeding decline in Great Britain.
  • Sheep numbers and Welsh Curlew looks at habitat associations within a large site  in the Welsh uplands; getting the grazing regime right seems to be very important.
  • Curlew Moon has at its heart a review of Mary Colwell’s book of the same name but also summarises some of the issues being faced by Curlew in Ireland and the UK.
  • Ireland’s Curlew Crisis focuses on the nationwide breeding survey between 2015 and 2017, which revealed a 96% decline in the number of pairs in just 30 years.
  • Curlews and foxes in East Anglia suggest that ‘curlew plots’ may be helpful in the fight to conserve the species.
  • More Curlew chicks needed has at its core a paper about survival rates of breeding and wintering Curlew. Even in a period of historically low annual adult mortality, breeding numbers have continued to fall.
  • The flock now departing reveals fascinating details about Curlew migration with descriptions of four occasions when two tagged birds ended up in the same migratory flock.

On autumn high tides, flocks of Curlew roost on east coast stubble fields (© Graham Catley)

On an autumn high tide, a flock of Curlew roosts on an east coast stubble field (© Graham Catley)


 GFA in Iceland

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

@grahamfappleton

UK Dotterel numbers have fallen by 57%

Research from RSPB Centre for Conservation Science, with University of Aberdeen (School of Biological Sceinces), Scottish Natural Heritage (SNH) and Natural Research Ltd

Male Dotterel brooding chicks: Alistair Baxter

Male Dotterel brooding chicks: Alistair Baxter

I have only once climbed a mountain to count Dotterel, with Phil Whitfield decades ago, but that is enough to appreciate how many hundreds of hours of hard work lie behind the statement, “The number of Dotterel breeding in the UK declined by over half between 1987/88 and 2011”. This is the headline in a paper published in the November 2015 issue of the BTO journal, Bird Study:

Changes in the abundance and distribution of a montane specialist bird, the Dotterel Charadrius morinellus, in the UK over 25 years. Daniel B Hayhow, Steven R Ewing, Alistair Baxter, Andy Douse, Andrew Stanbury, D Philip Whitfield & Mark A Eaton Bird Study 62:4, 443-456

As Des Thompson and Phil Whitfield wrote at the conclusion of their account for the 1988-91 Breeding Atlas, “The Arctic affinities of the British Dotterel, its beauty, its rarity and its likely sensitivity to habitat and climate change secure its place as one of our most fascinating breeding birds”.  Well-documented stories of females laying clutches in Scotland, to be brooded by their male partners, and then flying on to Norway to lay second clutches add an air of mystery too.

The 2011 Dotterel Survey was carried out under the Statutory Conservation Agencies/RSPB Annual Breeding Bird Survey (SCARABBS) programme and was funded by the RSPB and SNH (Alistair Baxter)

The 2011 Dotterel Survey was carried out under the Statutory Conservation Agencies/RSPB Annual Breeding Bird Survey (SCARABBS) programme and was funded by the RSPB and SNH (Photo: Alistair Baxter)

The population estimate of 423 breeding male Dotterel in 2011 represents a decline of 43% since 1999, when the comparable total was 747 pairs, and of 57% since 1987/1988 (981 pairs).  All regions except the West Highlands had lower numbers in 2011 than in 1999, with the core area of the East Highlands (the Grampians east of the A9) experiencing a significant decrease of 32% since 1999 and 56% since 1987.  This massif has become increasingly important, with 60% of the pairs in what amounts to 30% of the potential breeding habitat for Scottish Dotterel.

No Dotterel were recorded outwith Scotland during the systematic national survey but Bird Atlas 2007-11 fieldwork did add a record from Northern England.  In the absence of annual monitoring, a national survey can only provide a snapshot for a species.  However, information gathered during the four summers of the Bird Atlas project and as part of an ongoing detailed study suggests that the results for 2011 are representative of the current UK Dotterel population – and that the declines are therefore very much real.

Population changes across the range

Large-scale surveys of Dotterel are difficult, due to the remoteness of many of their breeding sites, and monitoring elsewhere across their European breeding range tends to be based on visits to particular sites or using transects.  Given the plasticity shown by the females – including an ability to nest in two countries in one year – changes in apparent numbers could potentially reflect the fact that birds breed further north in some springs than in others.  The best series of data come from Swedish Lapland, where Svensson & Anderson reported no changes in the population over the period 1972 to 2011.

In, Finland, Pulliainen & Saari observed that most females left their study area after egg-laying and hypothesised that this was in order to secure more mates further north. Lucker et al. have found evidence for higher rates of shared incubation by females at the more northern extent of the species’ breeding range than those breeding further south, providing some evidence to support this hypothesis.  Saari had previously estimated the Finnish population to be 90% less than in the early 1900s and suggested that hunting in early 20th century and overgrazing by reindeer may have been to blame.   Since the 1960s, the tree line has advanced and large areas of the mountain heath are now covered by scattered Scots Pines, making the habitat largely unsuitable for Dotterel.  Similar processes, associated with warmer conditions, could have major, negative impacts the number of Dotterel breeding in Scotland.

Is the SPA network working for Dotterel in Scotland?

Racomotrium heath is an important and increasingly rare habitat (Alistair Baxter)

Racomotrium heath is an important and increasingly rare habitat (Alistair Baxter)

The designation of Special Protected Areas (SPA), based on the results of the 1987/88 survey has been a key tool in the efforts to conserve Dotterels in Scotland.  This network of montane sites has helped to provide a focus for research funding and planning considerations.  Encouragingly, SPAs have supported between 50% and 60% of the population since designation.

The decline in numbers of Dotterel within and outwith the SPA network is of concern, but in terms of site occupancy, sites in SPA/SSSIs were more likely to be occupied than those outside the protected area network.  Protected area designation has been shown to be good for a group of northern species at the trailing edge of their distribution in the UK, although this effect decreased at higher latitudes and altitudes (Gillingham et al. 2015).

Explaining the declines

The well-referenced, discussion section of the paper looks at the potential reasons for the changes to Dotterel populations and assesses the available evidence.

Habitat change in the high mountains: Racomitrium moss heath has been shown to provide important foraging opportunities for Dotterel of all ages; this is a habitat that has been in a long-term decline over the last half century.   Studies have outlined how overgrazing and levels of atmospheric nitrogen interact, resulting in changes to the composition and extent of montane heaths.

A frequent prey of both adult and juvenile Dotterel is Tipulid (cranefly) larvae which require dense mats of moss vegetation.  Changes in composition and extent of Racomitrium heath could result in reduced prey availability, potentially affecting settlement decisions and breeding success for Dotterel.

Raven abundance has increased across much of the Dotterel's range (Map from Bird Atlas 2007–11, which is a joint project between BTO, BirdWatch Ireland and the Scottish Ornithologists’ Club)

Raven abundance has increased across much of the Dotterel’s range (Map from Bird Atlas 2007–11, which is a joint project between BTO, BirdWatch Ireland and the Scottish Ornithologists’ Club)

Predation in the breeding season: Predation of Dotterel eggs by Ravens can cause localised declines, and lower return rates have been reported for adult male Dotterel after clutch loss by predation. The period of decline in Dotterel is coincident with an increase in range and abundance, of Ravens in Scotland.  Although previous work has found no significant negative associations between Raven numbers and upland wader populations, this interaction may well warrant further investigation.

Disturbance: There is little strong evidence for widespread effects of increased visitor numbers, despite negative impacts of such activities on heath condition.

Pressures in wintering areas: Pesticide use and hunting on the wintering grounds, North Africa and Spain, have been suggested as possible factors in the decline.

More attractive conditions further north: Upland species, such as Dotterel, are cold-adapted and may well find northerly areas more conducive to breeding.  Without a flyway approach to Dotterel monitoring it is not possible to distinguish between a northerly shift in the breeding area of Dotterel and population-scale declines.

What next?

The 2011 Dotterel survey clearly shows the decline in numbers of Dotterel breeding in the UK and contraction to core sites in the East and Central Highlands.  Further, detailed work is required to understand the mechanisms driving the observed population trends, which may well involve studies in wintering areas and migration hot-spots, as well as a mixture of ecological research and ongoing monitoring in the mountains of Scotland.

The 2011 Dotterel survey has provided a spring-board for detailed research by Alistair Baxter, which is being written up as part of his PhD at the University of Aberdeen.  By repeating studies carried out during the 1980s by SNH, he hopes to see whether changes in habitat availability, habitat quality and invertebrate abundance can help to explain the decline in numbers in the last thirty or so years.

Ptarmigan is another montane species that will be targeted by

Ptarmigan is a key montane species that is being targeted by “What’s Up?” (Alistair Baxter)

Given how much effort has to go into any survey of upland species and the relative infrequency of national surveys, it is great that two recent initiatives are making the most of the calories burned to climb our highest peaks.  Many volunteers involved in the annual Breeding Bird Survey of upland squares now add an adjacent square to the original, randomly-selected plots, in order to increase the sample size in these sparsely populated but special bird areas.  Another valuable contribution is being made by mountain-lovers who know their birds and who are now contributing to the BTO Scotland led “What’s Up?” project.  This focuses on species that are sensitive to climate change and disturbance, such as Ptarmigan, Snow Bunting and Dotterel.

In an era of ever tightening budgets, it is unclear when it might be possible to organise another national survey for Dotterel.  Let’s hope that, until then, “What’s Up?” can help to alert us to distribution changes and that annual surveys of key sites might provide indications of national population changes. 

Dotterel was moved onto the red list of species of conservation concern on 3 December 2015.


 GFA in Iceland

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

@grahamfappleton

Conserving British-breeding Woodcock

To help to take the pressure off declining and now red-listed British-breeding Woodcock, many estates are already delaying the start of the Woodcock shooting season.  How might this make a difference?

This is a modified version of an article published in Shooting Times on 30 Sep 2015. There are updates at the end, reflecting changing advice provided by the Game & Wildlife Conservation Trust.

Photo: Richard Chandler

Photo: Richard Chandler

Each autumn, the British population of Woodcocks is swamped by the arrival of up to a million birds, returning from northern Europe and Scandinavia. The exact timing of their migration is very much influenced by weather, with birds crossing the North Sea as early as October or as late as December.  The numbers each year are thought to vary markedly, reflecting peaks and troughs in the size of the European breeding population, annual chick production, the amount of frost and snow on the other side of the North Sea and the timing of periods of cold weather.

A quick look at the bag index for Woodcock, produced by the Game & Wildlife Conservation Trust (GWCT), shows annual variation in the numbers shot each winter but no downwards trend.  Hunting appears to be sustainable (but see note at the bottom giving advice from GWCT about shooting in winter of 2017/18).  Unfortunately, there is a problem; British-breeding Woodcock are in serious decline and there is no way to differentiate between a local bird and one from continental Europe.  As the GWCT Woodcock tracking project has shown, birds share the same woodland habitats during winter months.  Mara and Jack, for instance, two birds caught in March 2014 on Islay, have very different annual stories to tell, with Mara breeding locally and Jack migrating to Russia.

A shrinking distribution

Bird Atlas 2007-11, published by the British Trust for Ornithology (BTO), confirmed that our Woodcock are in trouble.  Between 1968-72 and 1988-91, the number of 10×10 km atlas squares where Woodcock were present fell from 1439 to 917, representing a decline of 36%.  By 2008-11, the number was down to 632, a further drop of 31%.  In the 1968-72 Atlas, Woodcocks were generally widespread, with birds absent only from parts of southwest England and Wales and easy to find from the North Midlands through to northern Scotland, other than in the highest mountains.  Fragmentation that was becoming apparent in 1988-91 was glaringly obvious in 2008-11, especially in the south and west.  In Ireland the situation, if anything, looked worse.

Bird Atlas 2007-11, published by the BTO, in association with the Scottish Ornithologists’ Club and BirdWatch Ireland, shows that breeding Woodcock are disappearing from southern and western Britain, as well as from Ireland. Downwards pointing black arrows show losses, with bigger symbols indicating recent changes.

Bird Atlas 2007-11, published by the BTO, in association with the Scottish Ornithologists’ Club and BirdWatch Ireland, shows that breeding Woodcock are disappearing from southern and western Britain, as well as from Ireland. Downwards pointing black arrows show losses.

Early results being contributed to the Bird Atlas 2007-11 project confirmed that there was an urgent need for a special Woodcock survey, to try to assess numbers as well as distribution, and this was organised for the summer of 2013.  The GWCT and the BTO wanted to replicate the survey they had organised in 2003, which suggested that the breeding population across Scotland, Wales and England included just over 78,000 territorial males.

Andrew Hoodless of GWCT has shown that the number of Woodcocks observed during a standard evening watch period provides a good index of local abundance.  The national survey called for the deployment of hundreds of birdwatchers, who were asked to visit chosen sites, many of which had been visited ten years previously.  Standing at dusk and listening to the distinctive roding calls of male Woodcocks, as they patrol the boundaries of their territories, provides magical moments for lucky birdwatchers.  However, the chance of success in many parts of the country was far lower in 2013 than it had been in 2003.  A paper, with a full regional analysis was published in 2015, revealing an estimated fall in numbers of 30%, to just over 55,000 roding males.  As suggested by the Atlas distribution maps, percentage losses were higher in Wales and England than in Scotland.

Current status and recent trend of the Eurasian Woodcock Scolopax rusticola as a breeding bird in Britain, by Christopher J Heward, Andrew N Hoodless, Greg J Conway, Simon Gillings & Robert J Fuller, in Bird Study Nov 2015

The main aim of the 2013 Woodcock survey was to assess the population, rather than to understand the causes of decline, but it is interesting to note that there were smaller losses in the largest areas of woodland.  More detailed studies have suggested that larger woods may offer a greater diversity of habitats and damper micro-climates in which to feed.  Booming deer populations are having major effects on a lot of woodlands; by browsing the vegetation they can open up the understorey, thereby removing nesting habitat and drying out soils.  There are probably several factors driving down the breeding population and it has been suggested that recreational disturbance and over-winter hunting of resident birds could each be playing a part in declines.

Changes to the hunting season?

BirdTrack is coordinated by the BTO, in partnership with RSPB, BirdWatch Ireland, the Scottish Ornithologists’ Club and the Welsh Ornithological Society. These lists provide fascinating information about the timing of migration, annual breeding patterns and species’ abundance. See www.birdtrack.net to learn more.

BirdTrack is coordinated by the BTO, in partnership with RSPB, BirdWatch Ireland, the Scottish Ornithologists’ Club and the Welsh Ornithological Society. These lists provide fascinating information about the timing of migration, annual breeding patterns and species’ abundance. See www.birdtrack.net to learn more.

Although the main pressures may well occur during the summer months, one way to help British breeding Woodcock may be to change the start of the shooting season.  The season currently opens on 1 September in Scotland and 1 October across the rest of the UK.

Looking at BirdTrack data, collected from species lists sent in by thousands of birdwatchers across Britain & Ireland, it is clear that there are virtually no continental Woodcock in these islands during September and few until at least the second half of October.  In the graph alongside, the red line shows average rates of occurrence on birdwatchers’ lists.  The blue line for 2014 indicated a pulse of arrivals in early October, largely as observed by birdwatchers on the east coast.  These birds will have moved inland and disappeared into woodland and farmland.  The main arrival in this particular year appears to have been in late October with later spikes in the graph suggesting further bursts of east coast activity in November and December.

The 2013 Woodcock survey was funded by the Game & Wildlife Conservation Trust, the Shooting Times Woodcock Club and a charitable trust. Photo: Richard Chandler

The 2013 Woodcock survey was funded by the Game & Wildlife Conservation Trust, the Shooting Times Woodcock Club and a charitable trust. Photo: Richard Chandler

The BirdTrack pattern will come as little surprise to gamekeepers and shoot-owners, many of whom already restrict Woodcock shooting to the winter months, in order to minimise losses of local, resident birds.  GWCT scientists have been encouraging restraint in the autumn months for some while.  Now, having analysed the results of the GWCT/BTO 2013 Woodcock survey, and shown a further decline of nearly a third in just ten years, they are researching the potential impact of shooting on resident birds. This will include an assessment of whether a formal change to the timing of the hunting season for Woodcock is required, in order to add an extra level of protection to resident birds.

Update: 28 July 2017

New GWCT  guidance: ‘generally we recommend not shooting woodcock before 1 December’ and not at all if ‘numbers have been low in the area’. More information is available at https://www.gwct.org.uk/media/696047/Pocket-woodcock-guide.pdf

Update: 11 December 2017

Migrant Woodcock appear to have had a poor breeding season and GWCT is advising restraint:

Dr Hoodless has issued the following statement: “GWCT and the Woodcock Network are advising shooters across the UK to rethink their woodcock shooting for this season and reduce their bags. This echoes moves being taken by organisations in several other European countries. A further update will be issued in early January, once more information is available.”

“Although similar events will have happened many times in the past, this is the first time that monitoring of woodcock age ratios by ringers, and improved communication across Europe, has been able to offer shooters an early warning system. Populations normally rebound after such events, but most shooters understand the importance of preserving breeding stocks when there are signs of adverse natural events and are prepared to minimize shooting pressure in order to aid population recovery.”

Read more here

Update: 16 March 2018

Woodcocks are severely affected by cold weather. Research by GWCT suggest that Woodcock start to suffer when the ground has been frozen for relatively short periods of time. They propose restraint after four days of freezing conditions, with birds being given a recovery period of seven days once a thaw commences. There’s more in this blog here and the paper can be found here.

Update: September 2020

There is no suggestion that the numbers of Woodcock breeding in Finland, Sweden and Norway are changing. This blog summarises survey data for breeding waders during the period 2006 to 2018.


 GFA in Iceland

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

@grahamfappleton

A helping hand for Lapwings

This article has been slightly adapted from one written for the Autumn 2015 edition of The Harrier, published by the Suffolk Ornithologists’ Group

Lapwing in flight: Richard Chandler

Lapwing in flight: Richard Chandler

The space-invader cries of displaying Lapwings are welcome signs of spring across much of Britain’s countryside and losses of this iconic species, especially in lowland England, have been well chronicled.  Conservation organisations, and the RSPB in particular, are successfully supporting breeding numbers on nature reserves but how can their interventions be replicated on working farms, without flooding fields and installing fox-proof electric fences?

On the look-out: Grahame Madge/RSPB impages

On the look-out: Grahame Madge/RSPB impages

Dr Jen Smart of the RSPB Centre for Conservation Science and Professor Jenny  Gill of the University of East Anglia have been studying breeding waders on  RSPB Reserves in the Norfolk Broads for over ten years, but more recently they have extended their wader research into commercially managed grasslands across Norfolk and Suffolk, using funding from Defra.  At the February 2015 ‘Foxycology’ conference, Dr Smart explained how the RSPB is trying to manage the conflict between the conservation of ground-nesting birds and foxes.  The RSPB does not rule out shooting as a protection measure – there’s active fox control in the study site – but prefers to adopt non-lethal solutions to the predation problem.  One answer may be to provide foxes with ‘convenience food’, in the form of mice and voles.  If it’s easier to find mice and voles than wader nests and chicks then perhaps that’s what foxes will do?

Predation is a natural process but rates can be severely skewed by the way that the countryside is managed, especially when the balance of predator and prey is disturbed.  Many predators are opportunists, with species such as foxes, crows, gulls and raptors switching their activities to take advantage of local food availability.  Seasonal abundance of food resources can affect both survival and productivity.  An inexperienced young fox must have a better chance of surviving the winter if he is presented with a generous supply of released pheasants, whilst a vixen, trying to raise a litter of cubs, will find easy pickings in a gull colony.  In the same way, a nature reserve that is full of nesting waders will often attract foxes during the breeding season.

By creating shallow ditches, which add water and insects to grassland habitats, Lapwing productivity is increased: Mike Page/RSPB

By creating shallow ditches, which add water and insects to grassland habitats, Lapwing productivity is increased: Mike Page/RSPB

The RSPB has become very good at increasing populations of wading birds breeding on their lowland nature reserves but staff are frequently frustrated by the low numbers of young birds that survive through to fledging in some years.  Adding water to the landscape, in the form of pools and ditches, attracts high densities of breeding waders, as these wet features provide insect-rich places to which adults can take their chicks.  The RSPB/UEA research team has found that Lapwing nests are far more successful when birds nest at high densities, presumably because they work together to look out for and drive off potential predators, and they also found that Redshanks benefit from the activities of the more numerous and defensive Lapwings.  Practical actions, such as clearing woodland that abuts wetland or removing single trees in which crows sit to spot the next meal, have been shown to reduce avian predation in the daytime, to such an extent, in fact, that three-quarters of nest-losses are now taking place at night.

Lapwing chick: Richard Chandler

A young and vulnerable Lapwing chick: Richard Chandler

Using cameras, the team has shown that 70% of the culprits filmed taking eggs are foxes, with badgers coming a distant second, at 12%.  Wader chicks leave the nest soon after hatching, and RSPB research has shown that chick predation is then largely from foxes at night and raptors in the daytime, but with stoats, weasels and opportunistic birds, such as grey herons, taking smaller numbers.  Overall, by far the biggest threat to productivity is the fox.

One fox (and badger) deterrent that is available on nature reserves is to use well-maintained mains-supplied electric fences to surround fields in which waders nest.  Trials by the RSPB have shown that Lapwing fledging success is significantly improved in fenced areas, increasing from just over 0.2 chicks per pair to 0.8 chicks.  The target level for a sustainable population is 0.6 young per pair so the lower figure is well below par and 0.8 should be providing a surplus of birds that can go on to nest elsewhere.  Fences are not perfect, however; they do not exclude predators such as stoats and weasels, and the increased success of nests means high densities of chicks can be an irresistible resource for opportunistic and adaptable aerial predators trying to feed their own young.  Fencing is also only really effective on a relatively small scale so does not provide the solution to what is a landscape-scale problem.  RSPB research has shown that there is a lot of variability in predation rates, which provides opportunities to try to understand the complex interactions between foxes, mustelids (stoats and weasels), small mammals and waders.

In open grassland, Lapwings can keep an eye out for approaching predators: Richard Chandler

In open grassland, Lapwings can keep an eye out for approaching predators: Richard Chandler

Much of the patchiness of productivity within a site is linked to the amount of grass in fields and along field edges.  Grazing is a key management tool in wet grasslands, with cattle creating the short and varied sward structure that is attractive to a range of breeding waders.  By using ink tracking tunnels, within which mammals leave their footprints, and looking for field-signs of activity, Dr Becky Laidlaw has been able to show that this short grass is of little use to mice and voles.  She discovered that they prefer verge areas, outside the fields, where the grass is at least 20 cm tall and where there is ground-level vegetation cover of more than 80%.  Using data on wader nest success collected over 10 years, she was also able to show that Lapwings nesting in fields close to this small mammal habitat had lower rates of predation. Adding in tall grass strips and patches within a farmland landscape could potentially increase the populations of small mammals, thereby distracting foxes and mustelids, and reducing predation pressure.  Avian predators of wader chicks might appreciate this intervention too!  This work is published as:

The influence of landscape features on nest predation rates of grassland-breeding waders by Rebecca A Laidlaw, Jennifer Smart, Mark A Smart & Jennifer A Gill in Ibis 157:4 Oct 2015

Over the last two years, the RSPB/UEA team has worked with landowners of commercial grasslands across East Anglia, who between them are responsible for a large percentage of remaining breeding wader populations. Building on the work on reserves, the aim was to understand whether habitat suitability and predation processes differ between reserve and wider countryside waders.  To accomplish this, they assessed the extent to which grassland management options within agri-environment schemes support small mammal populations, as well as measuring field wetness, Lapwing densities and nest predation rates.  They also assessed the importance of different nest predators for waders nesting in the wider countryside and within nature reserves.

A weasel leaves its mark: Becky Laidlaw

A weasel leaves its mark: Becky Laidlaw

Becky and her team found similar distributions of small mammals in the wider countryside as had already been found on nature reserves.  Within both, there were higher densities of small mammals within grassland habitats outside of fields, while presence within fields did not vary significantly among fields managed under different grassland agri-environment options.  Encouragingly, densities of Lapwing nesting in fields managed in accordance with the breeding wader option were significantly higher than in fields with no interventions. Lapwings nesting in areas with many other Lapwings and nests that were closer to patches of small mammal habitat were less likely to be predated, but the rate of Lapwing nest predation did not differ between the wider countryside and reserves.  It should be possible, therefore, to create Lapwing hot-spots outside of nature reserves, thereby expanding the reproductive potential of East Anglia.  Unsurprisingly, given the previous findings about the causes of nest-losses on nature reserves, wider-countryside sites where foxes were present experienced both higher overall nest predation and nocturnal nest predation.

Redshank also benefit for management designed to support Lapwings and probably appreciate the shared look-out duties Photo: Richard Chandler

Redshank also benefit for management designed to support Lapwings and probably appreciate the shared look-out duties Photo: Richard Chandler

The main findings of this study are that wader nest predation rates and spatial patterns of nest predation on lowland wet grasslands are remarkably similar inside and outside reserves. This should help to directly inform the design and development of lowland wet grassland landscapes, making them capable of attracting and supporting sustainable populations of breeding waders within the constraints of commercial grasslands.  Jen Smart is optimistic; “If we can provide wet fields that look attractive to Lapwings in spring and patches of tall vegetation that hold high numbers of small mammals it ought to be possible to improve nesting success and productivity”.  She and her colleagues are now looking at how a range of different agri-environment options might be used to create such landscapes.  The next phase of the project will be to try out the most promising options, in order to see the scale at which these patches of tall vegetation for small mammals need to be provided if they are to deliver the desired result – more breeding waders.

Update 

The are several other WaderTales blogs that may be of interest to people who like Lapwings:

For a full list of WaderTales blogs visit https://wadertales.wordpress.com/about/

 


 GFA in Iceland

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

@grahamfappleton