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.

On the beach: breeding shorebirds and visiting tourists

Rising sea levels, stormier weather, coastal development and more people are putting increasing pressures upon shorebirds that nest on beaches. A paper about the breeding waders of Norfolk & Suffolk (UK) coasts illustrates the importance of understanding human behaviour when trying to maintain (or create) space for breeding plovers. This paper will be of particular interest to conservationists trying to support breeding populations of species such as Ringed Plover, Kentish Plover, Piping Plover and Snowy Plover.

The problems of disturbance

Around the globe, nesting plovers are being threatened by human disturbance. Local initiatives to reduce these impacts include the installation of electric fences, recruiting volunteer wardens and changing local bylaws. You can learn more about which interventions work from Conservation Evidencethere’s more about this at the end of this blog.

Panning out, to look at the bigger picture, is it possible to determine where conflicts between breeding birds and tourists are likely to occur, so that one can try to resolve the problems before they start? Can this information help to inform planning decisions?

Oystercatcher with chick

Ringed Plovers and Oystercatchers

The coastline of Norfolk and Suffolk should be an ever-changing environment, dominated by sand and shingle beaches. Coastal defences artificially maintain the barrier between sea and land but sea-level rise is predicted to over-top and destroy sea walls during storm events. How will East Anglia’s beach-nesting waders cope with squeezed beaches at the same time as East Anglia is seeing increasing tourist numbers? In a 2020 paper in Global Ecology & Conservation, Jamie Tratalos and colleagues from the University of East Anglia investigated the distributions of nesting Ringed Plovers and Oystercatchers around the beaches of Norfolk and Suffolk, relating settlement patterns to visitor numbers.

Snettisham beach – sunny weather is not great for the local breeding Ringed Plovers

Ringed Plovers and Oystercatchers breed on sand and shingle beaches that are also attractive to people. They are prone to disturbance, especially by dogs that are allowed to run free, as discussed by Gómez-Serrano (2021). Nests can be trampled, incubation can be interrupted and chicks can be killed. Liley and Sutherland (2006) showed that, over a 9 km stretch of Norfolk coastline, Ringed Plovers bred less successfully when exposed to disturbance by beach visitors, and population declines in this species have been linked to human disturbance (Birds in England by Brown & Grice, 2005). Human recreation has also been shown to be associated with reduced breeding success in Eurasian and other oystercatcher species (Tjørve & Tjørve, 2010), and Ens and Underhill (2014) suggest that increased human use of the coastal zone, combined with increased risk of nest flooding and loss of wetlands, may threaten the conservation of oystercatchers around the world.

Ringed Plovers can have several breeding attempts in the course of a summer

UK breeding populations of Ringed Plover have declined in recent decades, from a conservative estimate of approximately 8400 pairs in 1984 to 4070 in 2007 (Conway et al., 2019) and the species is now red-listed (see the WaderTales blog: Nine red-listed UK waders). Oystercatchers have undergone considerable Europe-wide decline in recent decades and the species has been classified as ‘Near Threatened’ globally (IUCN, 2020).

Counting birds and people

In 2003, when the study at the heart of the Tratalos paper was carried out, East Anglia’s beaches between the Wash and the River Stour held about 3% of the UK’s breeding Ringed Plovers, as well as relatively small numbers of breeding Oystercatchers. As part of a bigger climate change research programme, Tratalos et al were keen to understand what drove the distribution of Ringed Plovers and Oystercatchers, in order to be able to include conservation actions in plans to manage the changing coastline of Norfolk and Suffolk, especially associated the abandonment of outer sea defences. Their research was written up in a 2020 paper in Global Ecology & Conservation.

In the study, the authors examined a 212 km stretch of coastline, mapping all breeding pairs of Ringed Plover and Oystercatcher, as well as the environmental characteristics of beaches. Data on the location of bird territories, and the habitats in which they were found, were collected by Dave Showler in the period between early April and mid-June in 2003. Details of survey methods can be found in the paper.

Map data from Bird Atlas 2007-11 (BTO, BirdWatch Ireland and SOC)

Visitor numbers to different beaches were assessed by filming from a light aircraft, flying at an altitude of 150 metres. 38,634 human visitors were mapped from three flights during sunny weekends in April, June and August, when the tide was at approximately mid phase. There were pronounced peaks in visitor numbers along the coastline, with 19 of the 1003 beach sections experiencing over 10 times the average number of visitors and 231 sections hosting none.

The key findings from surveys and analyses were:

  • Of just over one thousand 200m sections of beach surveyed, 183 beach sections contained Ringed Plover territories (266 breeding pairs) and 117 contained Oystercatcher territories (223 pairs).
  • There were more occupied territories in less-visited areas, for both species. See table relating the visitor index to occupation of sectors. An index of 0.13 means that visitor numbers were 13% of the mean across all sectors.
  • No Oystercatchers were found breeding in sectors where the visitor index was higher than 2.8. No Ringed Plovers were found in sectors where the index was above 5.5.
  • Ringed Plovers territories were more common in sections that had dunes at the back of the beach and where the beaches were broader at low tide.
  • Oystercatchers appeared to need space above the high-water mark, as well as a broad intertidal area.

The associations between territories and habitat enabled the team to predict the number of pairs of waders that might have been present in areas which were highly impacted by visitors. If visitor numbers were reduced to zero across the whole study area, breeding potential could be hugely increased.

Feeding on the mud at low tide – Ringed Plovers and Oystercatchers need a broad intertidal area
  • The authors predict that there would have been an additional 90 beach sections where Ringed Plovers could potentially establish territories, suggesting that tourism and the local use of beaches has already removed 33% of Ringed Plover breeding habitat.
  • There were 96 sections where breeding Oystercatchers might have been expected to be found, so they have already lost 45% of potential habitat.

Practical considerations

These results suggest that human activity on beaches influence the location of breeding territories of Ringed Plovers and Oystercatchers, with both species using territories where the number of human visitors was relatively low, when considered both at the scale of the whole Norfolk and Suffolk coast, and locally within areas of this coastline.

In the absence of people, there appear to be clear features of the areas that determine if sectors are used by both wader species for breeding. This makes it possible to predict places where increased access could cause problems so that, ideally, tourism might be encouraged in areas that are less likely to be used by breeding waders. Unfortunately, the beaches that are great for red-listed Ringed Plover – with a back-drop of sand dunes, a sandy beach to walk along at high tide and a gently-shelving intertidal area – are also ones that attract people. This makes it harder to create discrete ‘people zones’ and ‘wader zones’ than might otherwise be the case.

Access points create issues for breeding wader but the effects of most visitors are localised. Unless birdwatching or exercising a dog, the typical tourist will not stray more than 300 metres from a carpark, as indicated in the graphic above. In less-disturbed beach sections, where Oystercatchers set up territories, chicks can hide in upper-beach vegetation until parents indicate that it is safe to come out to be fed.

When Emma Coombes (Global Environmental Change, 2009) asked visitors to Norfolk’s beaches what they were looking for, there was a remarkable consistency in the responses from dog-walkers, sun-bathers and birdwatchers. They all wanted to be on remote flat, sandy beaches, with sand dunes. They would appreciate a car park and toilets too. As soon as such facilities are provided, of course, visitor numbers increase, the remoteness is lost and so are breeding waders, unless fences and wardens are introduced.

Winterton-on-Sea beach is promoted as a tourist location with access to a national nature reserve

Planners have few tools available to them, when it comes to protecting stretches of coastline. All that they can control is development (e.g. new roads, housing and tourist accommodation) and facilities such as car parks and toilets. This paper clearly shows the need to understand the local features that are needed by nesting waders and the importance of documenting current distributions, so that local and national planning authorities have the information they need when planning for the future.

Paper in Global Ecology & Conservation

Vulnerable Ringed Plover chick

Regional models of the influence of human disturbance and habitat quality on the distribution of breeding territories of common ringed plover Charadrius hiaticula and Eurasian oystercatcher Haematopus ostralegus. Jamie A. Tratalos, Andy P. Jones, David A. Showler, Jennifer A. Gill, Ian J. Bateman, Robert Sugden, Andrew R. Watkinson & William J. Sutherland.

Conservation evidence

Before trying a new conservation technique on a local patch, it is worth checking out what has been tried elsewhere. A quick visit to the Conservation Evidence website and a search on ‘beaches’ and ‘bird conservation’ produced a list of 26 actions that have been written up in papers or grey literature. Although many of these interventions are more appropriate to tern conservation than shorebird conservation, a few seem to be particularly relevant to people who are considering how to help breeding Charadrius plovers. Five potential actions are assessed as ‘likely to be beneficial’

  • Use signs and access restrictions to reduce disturbance at nest sites
  • Physically protect nests with individual exclosures/barriers or provide shelters for chicks of waders
  • Protect bird nests using electric fencing
  • Physically protect nests from predators using non-electric fencing
  • Physically protect nests with individual exclosures/barriers or provide shelters for chicks of ground nesting seabirds
Dogs cannot read ‘no entry’ signs, designed to save space for breeding waders and terns

The Conservation Evidence website aims to make scientific research available to conservation practitioners. Anyone considering any of the interventions listed above can see a quick synopsis of what worked (and what didn’t work) in which circumstances. Anyone who has discovered another successful management technique is urged to write up their study – so that it can be added to the database.


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.

Waders on the coast

The UK’s coastline is of international importance because of the numbers of waders that it supports. In winter it accommodates over a third of Europe’s wintering Oystercatcher, Ringed Plover, Bar-tailed Godwit and Knot, as well as an increasing number of Sanderling.

Wintering waders on the UK’s estuaries are counted every month but those on the 17,000 km of open coast are only counted once a decade. There are good reasons for this disparity, given the much higher development pressures on estuaries and the need for regular monitoring of sites that are designated and protected. However, this does mean that we have very little information about wintering Purple Sandpipers, the vast majority of which are not covered by monthly Wetland Bird Surveys (WeBS). Over three-quarters of the UK’s Ringed Plovers are missed too, along with over half of the Sanderling and Turnstones and nearly half of the Curlew.

The last Non-estuarine Waterbird Survey took place during the winter of 2015/16, as discussed in the WaderTales blog NEWS and Oystercatchers. Jenny Gill and I undertook counts on Great Cumbrae and along stretches of the Clyde coast, in Scotland, an area we had also covered for the 2006/07 survey. We were concerned to count only 84 waders in 2015, compared to 206 in 2006. Details are in the table alongside. We hoped that 900 other people, walking along a total of 9000 km of the UK’s coastline, had been more successful!

The paper summarising NEWS results for the whole of the UK and making comparisons with previous surveys in 1997/98 and 2006/07 was not published until 2021. In the intervening period, the counts were included in two papers about wintering populations of waterbirds in Great Britain and Ireland, that were discussed in Do population estimates matter? and Ireland’s wintering waders. This blog draws heavily on a Twitter thread from the Wetland Bird Survey and the BTO’s press release. The new paper is published in Bird Study.

The big picture

In December 2015 and January 2016, NEWS III volunteers walked along amazing, long, white beaches, surveyed rocky headlands and scrambled the lengths of boulder-strewn coves. Not every kilometre of the coast could be visited but the fact that 50% coverage was achieved meant that estimates could be made of the whole coastline of the United Kingdom, together with the Isle of Man and the Channel Isles.

In terms of absolute numbers, Scotland has consistently supported the majority of the population across all non-estuarine waterbird surveys for Oystercatcher, Ringed Plover, Golden Plover, Lapwing, Purple Sandpiper, Bar-tailed Godwit, Curlew, Redshank and Turnstone. Although this is likely to reflect the relative length of the coastline for Scotland (12,714 km) compared to England (2,705 km), Wales (1,185 km) and Northern Ireland (328 km), Purple Sandpiper, Curlew, Redshank and Turnstone still appear to show a bias towards Scotland.

Using the information collected during the survey, BTO scientists were able to extrapolate estimates of the numbers of open-coast waders in the different countries of the UK and its island dependencies (see table below). The results are published in the journal Bird Study and summarised in the table below.

To evaluate the potential importance of the open coast, NEWS estimates for Great Britain in 2015/16 were compared to average population estimates. For eight species, the open coastline accounts for over 20% of the winter population. The figure of 113% for Purple Sandpipers suggests that more birds may have been present on the coasts of the UK in 2015/16 than in an average year or that the population estimate needs to be revisited. There are no Lapwings or Golden Plover in the table below, as there is no recent, reliable estimate of the national wintering population for either species. The Greenshank line is in italics as the sample size is small.

Ten species are considered in detail in the following sections. The maps were downloaded from the BTO website on 20 March 2021 (https://www.bto.org/our-science/projects/ringing/publications/online-ringing-reports). Comparisons are made between results from the Wetland Bird Survey (WeBS) and the Non-estuarine Waterbirds Survey (NEWS).

Oystercatcher

26% use open coasts. 21% NEWS decline since 1997/98. (WeBS decline 22%).

In December 2015, as we walked around the coast of Great Cumbrae in the Firth of Clyde, pairs of Oystercatchers were already staking out their territories, probably not having travelled anywhere since the previous summer or perhaps even in the last twenty years! Wintering flocks that we saw may well have included breeding birds from inland sites in Scotland, from Iceland and from Norway, together with juveniles and non-breeding sub-adults. NEWS III found that densities of coastal Oystercatchers were highest in Wales but that this is the area in which there had been the biggest declines. Breeding numbers have fallen rapidly in Scotland, as you can read in Oystercatchers: from shingle beach to roof-top.

Lapwing and Golden Plover

There was a 68% drop in Lapwing figures between 1997/98 and 2015/16 and a 59% drop in Golden Plover. NEWS and WeBS counts of Lapwing and Golden Plover are difficult to interpret because birds move readily between the coast and inland fields, in response to local conditions such as lying snow and the wetness of fields. This is further complicated in more prolonged freezing conditions, when flocks of Lapwing fly west and south in search of feeding opportunities.

Grey Plover

3% use open coasts. 71% NEWS decline since 1997/98. (WeBS decline 41%).

The Grey Plovers that we see around the coasts of the UK in December and January breed in Siberia. It has been suggested that one of the reasons for the decline in numbers in Britain & Ireland may be related to new generations of youngsters settling in winter locations on the continental side of the North Sea – a strategy that may now work better, given that winters are not as harsh. It is interesting that losses on open coasts, which many would consider sub-optimal habitats, have been more marked than on estuaries. There’s a WaderTales blog about Grey Plovers.

Ringed Plover

82% use open coasts. 21% NEWS decline since 1997/98. (WeBS decline 47%).

Ringed Plovers are red-listed in the UK because of the decline in winter numbers and the importance of these islands of the hiaticula race. In NEWS III, the vast majority of UK birds were found in Scotland (see earlier table) but densities were highest around the coast of England.  Colour-ring studies in Norfolk showed that breeding individuals can adopt a range of migration plans – some marked birds never left the county and others had winter homes as far away as France, Scotland and Ireland. This dispersal is pretty typical of hiaticula race Ringed Plovers that nest in western Europe and southern Scandinavia. Other races travel very long distances (Well-travelled Ringed Plovers).

Curlew

42% use open coasts. 40% NEWS decline since 1997/98. (WeBS decline 26%).

Large numbers of Curlew arrive in the UK in the autumn, with a strong link between Finland and the estuaries of England and Wales. It is estimated that 20% of Europe’s Curlew winter within the British Isles and any change in numbers has significance for a species that is already listed as near-threatened by BirdLife International. The decline in numbers on open coasts has been greater than that seen in estuaries; it has been suggested that this may relate to the breeding origins of birds using different habitats.

Bar-tailed Godwit

15% use open coasts. 33% NEWS decline since 1997/98. (WeBS decline 21%).

Unlike Black-tailed Godwits, which seek out the gloopiest of mud, Bar-tailed Godwits are perfectly at home on sandy shorelines. Wintering birds are of the race lapponica; these breed in Northern Scandinavia, Finland and western Russia (more here). NEWS III tells us that there has been a larger decline in numbers in coastal areas than on estuaries, perhaps related to the relative suitability of the two habitat types.

Turnstone

68% use open coasts. 29% NEWS decline since 1997/98. (WeBS decline 29%).

Almost all of the UK’s wintering Turnstones are thought to be birds that breed in Greenland and Canada. Declines are consistent between NEWS and WeBS. A Northumberland study has shown that, as numbers have dropped, so birds have withdrawn into areas that are less disturbed by people and dogs (See Disturbed Turnstones). About three-quarters of the UK’s open-coast Turnstones are found in Scotland but they are more thinly spread here than in England.

Sanderling

69% use open coasts. 26% NEWS increase since 1997/98. (WeBS increase 8%).

As discussed in Travel advice for Sanderling, the UK is a pretty good place to spend the winter. Whether the same would have been true for previous generations of Sanderling, that were faced with much colder winters, is open to conjecture. Since 1997/98, the densities of Sanderling in Wales have increased by 712%, by 462% in Scotland and by 85% in England. How long will it be until Sanderling flocks successfully over-winter in Iceland?

Dunlin

6% use open coasts. 51% NEWS decline since 1997/98. (WeBS decline 38%).

Three races of Dunlin can be seen in the UK (as you can read in Which wader, when and why?). Wintering Dunlin are birds of the alpina race, arriving in the UK from Siberia, NW Russia, northern Finland and northern Scandinavia in the late summer. Open coasts around the UK are estimated to accommodate fewer than 20,000 Dunlin. To put this into context, there are six estuaries that each hold more than this total during the winter period.

Purple Sandpiper

Almost all on open coasts. 19% NEWS decline since 1997/98. (WeBS decline 34%).

The rocky coasts of the UK are home to Purple Sandpipers from the Arctic, with a suggestion that North Sea coasts south of Aberdeen mainly play host to birds from Spitsbergen and northern Scandinavia, with Greenland and Canadian birds more likely to be found further north and on the Atlantic coast. Coastal numbers have declined by 19%. The Highland Ringing Group has shown that the number of young Purple Sandpipers has been declining on the Moray Firth, suggesting a period of relatively poor breeding success for birds migrating from the northwest.

Redshank

22% use open coasts. 42% NEWS decline since 1997/98. (WeBS decline 21%).

Perhaps surprisingly, few Redshank cross the North Sea to spend the winter in the UK. Winter flocks are largely made up of home-grown birds and migrants from Iceland. The recent decline in Redshank numbers is thought to be a reflection of changing numbers of British and Irish breeders, although there are no monitoring schemes to provide information about Icelandic birds. Since 1997/98, the number of Redshank on open coasts has dropped by 42% but almost all of the losses have occurred in the period since 2007/08 (37% decline between 2007/08 and 2015/16). Redshank is currently amber-listed in the UK, reflecting falling breeding numbers, but ‘promotion’ to the red list cannot be far off. There is a WaderTales blog about the rapid decline in the number of Redshank breeding on salt-marshes: Redshank – the warden of the marshes.

Summary

The Non-estuarine Waterbird Survey 2015/16 revealed that there have been major declines in abundance of four species since NEWS II in 2007/08, only eight years previously: Lapwing (down 57%), Curlew (down 31%), Redshank (down 37%) and Turnstone (down 32%). Lapwing and Curlew are both red-listed in the UK. The only species to increase is Sanderling (up by 79%).

Given the magnitude of the changes revealed in NEWS III, it is unfortunate that this labour-intensive survey can only be carried out every eight to ten years. Ideally, it might be possible to survey at least a sample of sites on an annual basis. It is certainly to be hoped that funding can be found for NEWS IV within the next few years, and that volunteers will once more be prepared to count waterbirds on beautiful, if exposed, stretches of coastline.

The results of NEWS III are published in a paper in Bird Study:

Wader populations on the United Kingdom’s open coast: results of the 2015/16 Non-Estuarine Waterbird Survey (NEWS-III) and a review of population trends. Humphreys, E.M., Austin, G.E., Frost, T.M., Mellan, H.J., Boersch-Supan, P., Burton, N.H.K. and Balmer, D.E.


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.

Where to nest?

pic whimbrelThere is nothing more obvious than an Oystercatcher sitting on his or her nest, but a brooding Snipe can be invisible until almost trodden upon. Which strategy works better: nesting in plain view but laying cryptically camouflaged eggs or hiding yourself and your nest in a clump of grass? Which species is most likely to hatch a successful brood of chicks and in what circumstances? In a 2020 paper in IBIS, Becky Laidlaw and colleagues analysed nest site characteristics and nest locations of 469 wader nests in Iceland in order to provide some answers

The perils of ground-nesting

pic hatching whimbrel

Hatching Whimbrel eggs, with the tell-tale shell fragments that signal a nesting attempt has been successful

Almost all waders are ground-nesters, which makes them highly vulnerable to a wide range of nest predators. To reduce the risks of predation, different strategies have evolved. In some species, nests are placed out in the open, and the camouflage is provided only by mottled egg colouration that resembles the background. In other species, nests are secreted in vegetation, meaning eggs and incubating adults are concealed from predators.

In both groups of species, the risk of nests being predated might vary, depending on the surrounding habitat. For open-nesting species, for example, clutches that are laid in large patches of similar habitat may be harder for predators to locate. The same could apply to closed-nest species that hide their nests; Snipe nests may be tricky to find in extensive areas of long grass but perhaps more at risk if there are only a few suitable clumps of long grass that predators need to check out.

pic hidden Redshank

Iceland: a wader factory

tableAs discussed in previous WaderTales blogs, particularly Do Iceland’s farmers care about wader conservation? Iceland is hugely important as a European ‘wader factory’. As farmland elsewhere has become less suitable for species such as Redshank and Snipe, the global importance of the country has increased (see table alongside for most recent figures from an AEWA report)  With this in mind, it is important to understand the factors that underpin the population dynamics of Iceland’s breeding waders.

Working in South Iceland, Becky Laidlaw and her co-authors tried to find as many nests as possible during the summers of 2015 and 2016. This area is largely a mosaic of open habitats, although there are more patches of forestry than there were twenty years ago. Most of the Southern Lowlands area is farmed, on a gradient between intensive and semi-natural, and this is reflected in the distribution of breeding waders (see Farming for waders in Iceland).

pic rope

Dragging a light rope across the vegetation to flush nesting birds

For this project, nests were located by surveys from vehicles and on foot, through observation of incubating adults, systematic searching, incidental flushing of incubating adults and rope-dragging (dragging a 25 m rope, held between two fieldworkers, lightly across vegetation) to flush incubating adults.

The analysis in the resulting paper in IBIS focuses on 469 nests of three open-nesting species (Oystercatcher, Golden Plover and Whimbrel) and three species that hide their nests in tall vegetation (Redshank, Snipe and Black-tailed Godwit). The team recorded the habitat and vegetation structure around each nest (at the nest, within a 5 m x 5 m square and in a wider 50 m x 50 m square) and worked out which nests hatched successfully and which were predated. The date and time of predation were determined, where possible, with nest-cameras providing extra information for some nests. Cameras captured nest-predation events involving Arctic foxes, Arctic Skuas, Ravens and sheep.

Interestingly, 2015 and 2016 were very different wader breeding seasons. The graphic below shows the mean temperatures for the months from April through to July (encompassing the wader breeding season at this latitude) were much cooler in 2015 than in 2016, representing average monthly difference of between 1.5°C and 2.5°C. At high latitudes these figures translate into very different rates of vegetation growth.

pic pretty graph

First, find your nest

When nests were first located, their positions were marked and referenced using GPS. Eggs were floated in water to provide an estimate of laying date and thereby predict hatching date. As the chick develops within an egg, the density of the egg falls. A newly laid egg will lie on the bottom of the flotation vessel. Over the next few days the ‘blunt end’ rises until the egg is still touching the bottom but vertical. Eggs in the late-development stage float ‘point-end-down’, with the latest eggs floating at an angle to the vertical (method described by Liebezeit et al.).

pic skua-ed goldie eggs

This Golden Plover nest was probably predated by an Arctic Skua

Nests were considered successful if one or more eggs hatched, and predated nests were defined as those that were empty in advance of the predicted hatch date or those without any eggshell fragments in the nest (a sign of successful hatching). To determine the time and date of nest failures, iButton dataloggers were placed in a randomly selected subsample of nests. These loggers recorded a temperature trace every ten minutes. A sharp and permanent decline in nest temperature below incubation temperature indicates nest predation. In both study years, motion-triggered cameras were deployed on a sample of open-nesting species to determine the predator species active on these nests.

When each nest was first located, the percentage of eggs visible from directly above the nest was estimated and the habitat surrounding each nest was assessed in the field at three spatial scales: the nest cup, the 5 m x 5 m and the 50 m x 50 m area surrounding each nest. Details are in the paper.

Which nests survive through to hatching?

Over the breeding seasons of 2015 and 2016, the outcomes of 469 wader nests were assessed. 259 hatched successfully (55%), 192 were predated (41%), 13 were abandoned, 7 were trampled and 2 were mown. A nest-loss rate of 40% is fairly typical for ground-nesting waders, when compared to studies in different countries and habitats.

pic fox attack

Daily nest predation rates did not vary significantly in relation to the habitat heterogeneity or the extent to which the dominant habitat covered the area surrounding the nest, at either 5 m x 5 m or 50 m x 50 m scales. Most clutches were laid in habitats that were the same or similar to the surrounding areas. Where there were differences, the dissimilarity between the habitat at the nest cup and in the surrounding area did not influence daily nest predation rates for open- or closed-nest species. Although nest predation is high, at about 40%, incidence of predation events appears to be unpredictable – or even random.

pic snipe nest

In cold spring conditions, Icelandic Snipe are not able to hide their nests

Daily nest predation rates were significantly higher for closed nests (Redshank, Snipe and Black-tailed Godwit nests) in which a greater percentage of the clutch was visible. This suggests that the onset and rate of vegetation growth could potentially constrain the availability of suitable nesting locations for these species, and hence influence nest success, particularly among early season nests. This has been studied in Icelandic Black-tailed Godwits by José Alves and colleagues and is described in From local warming to range expansion.

For closed-nest species, the visibility of nests was significantly greater during the early part of the 2015 breeding season, when compared to 2016, due to slower grass growth in cooler conditions.  The higher predation rate of more visible nests of closed-nesting species was apparent even though nests were predated up to three weeks after egg visibility was measured. These findings suggest that early nesting attempts by concealed-nest species are unlikely to be successful in years when vegetation growth is delayed or slow. There can be major benefits of hatching early, with recruitment into breeding populations typically being lower for later-hatched chicks, so vegetation growth rates are likely to be really important to species that conceal their nests (Redshank, Snipe & Black-tailed Godwit in this study). However, given the ongoing trend for warmer springs at subarctic latitudes, the conditions in which early nests can only be poorly concealed are likely to be reducing in frequency.

In summary

pic goldie nest in habitat

Golden Plover nest set within a homogeneous habitat matrix

Perhaps surprisingly, nest predation rates were similar for open-nest and concealed-nest species and did not vary with vegetation structure in the surrounding landscape. However, nest-concealing species were about 10% more likely to have nests predated when the nests were poorly concealed, and the frequency of poorly concealed nests was higher at the start of the breeding season in colder conditions.

The paper at the heart of this blog is:

Vegetation structure influences predation rates of early nests in subarctic breeding waders. Rebecca A. Laidlaw, Tómas G. Gunnarsson, Verónica Méndez, Camilo Carneiro, Böðvar Þórisson, Adam Wentworth, Jennifer A. Gill and José A. Alves. IBIS. doi:10.1111/ibi.12827

pic sheep


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

 

 

Which Icelandic Oystercatchers cross the Atlantic?

blog ringed birdMost Icelandic Oystercatchers leave Iceland in the autumn, crossing the Atlantic and arriving in Ireland, the UK and mainland Europe. Despite much shorter day-length and colder conditions, 30% spend the winter in Iceland, as discussed in this blog (Mission Impossible).

A 2020 paper from Verónica Méndez and colleagues asks whether birds that stay in Iceland or cross the Atlantic differ in sex, body-size or breeding location (within Iceland) and whether birds behave differently in different years. Interestingly, they were also able to test whether there is assortative mating – do Oystercatchers that stay in Iceland pair with other stay-at-home birds?

Iceland’s Oystercatchers

Iceland lies at the northern edge of the breeding range of Eurasian Oystercatchers. The country supports an unusually high proportion of wintering Oystercatchers, given its latitude and winter temperatures (Þórisson et al. 2018), and this may be influenced by the trans-oceanic flight of at least 700 km that migratory individuals must undertake to reach the European wintering sites. Individuals that migrate or stay within Iceland could differ in body size, for example if size influences the capacity to survive adverse winter conditions. Females tend to be slightly larger, and thus any sex differences in migratory behaviour could potentially reflect differences in body size.

It would be easy to imagine a scenario in which Oystercatcher pairs try to breed as early as possible, as this could increase the number of potential nesting attempts, as discussed in Time to nest again, based on Morrison et al. 2019. Does this mean that stay-at-home birds pair off at the start of the season, before migrants arrive? Given that most birds will choose the same mate in successive years, what happens in mixed pairs if a resident is waiting around for a delayed migrant? Is divorce likely to occur, as discussed in the importance of synchrony for Black-tailed Godwits, and could this mean that mixed pairs are rare?

Colour-marks and isotopes

blog map of sightingsA huge amount of the evidence that was used to answer the questions posed by Verónica and her colleagues was provided by volunteer birdwatchers, who reported colour-ringed Oystercatchers in their wintering areas, in the period through to April 2018. There’s an impressive set of dots on the map alongside, from the north of Scotland through to Spain, and the number of sightings continues to rise. It’s perhaps unsurprising, given the direction of travel from Iceland, that there is a strong westerly bias to the distribution across the British Isles.

The sample size from colour-ring observations was not big enough to answer all of the questions posed above, especially relating to whether pairs mate assortatively. To provide one data-point, it’s necessary to know the winter locations of both members of the pair. Might feather isotope ratios provide some help?

Oystercatchers that winter in Iceland use a restricted number of coastal sites (as inland sites are frozen during winter) and forage on marine prey. Elsewhere in Europe, a much wider range of marine and freshwater resources is available, with birds readily moving between the shoreline and fields, golf-courses, football pitches and road-side verges. Previous studies have shown that terrestrial diets produce different carbon and nitrogen isotope ratios, based on salinity and trophic level of prey items.  Are differences in habitat use and diet of Oystercatchers reflected in carbon (δ13C) and nitrogen (δ15N) isotope ratios of feathers grown during late winter?

blog isotope chest

Oystercatchers moult their chest feathers in late winter

The research team hoped that isotopic signatures from resighted colour-marked migrants and residents would be sufficiently different to be able to predict the probable wintering areas (Europe or Iceland) of marked birds not seen away from their breeding sites. If so, this would greatly increase the sample size, by enabling the combination of data from observations of colour-marked individuals with information on birds that could be assigned as Icelandic or European winterers using the isotopic composition of their feathers. They predicted that it would then be possible to:

  • Identify migratory strategies of individual Oystercatchers and explore whether the likelihood of migrating or staying in Iceland is related to gender, body size or breeding location.
  • Assess how consistent these individual strategies are between years.
  • Quantify spatial variation in the distribution of migrants and residents across the Icelandic breeding range.
  • Determine whether Oystercatchers mate assortatively in relation to migratory behaviour.

The work covered in this paper was conducted between 2013 and 2017. Full details of the study areas and methods are available in the paper – link below.

blog snow

Early nesting is not always a good idea – still incubating after sudden snow-fall

Migrant or resident?

blog co sligo

An Icelandic Oysterctaher spending the winter in Co. Sligo in Ireland

Of the 537 colour-ringed adults in the study, 58 were seen away from Iceland and 55 were shown to be resident in Iceland. Oystercatchers undertake a partial moult at the end of the winter period, when they grow new feathers on the neck and chest. The isotopic signature of a tiny piece of one of these feathers, taken from each adult at the time of ringing or recapture, was determined. The values of δ13C, which relates to habitat salinity, and δ15N, which relates to trophic level of diet, varied between residents and migrants but there was an overlap (details in paper).  There was enough of a difference, however, for it to be possible to allocate two-thirds of ringed birds that had not been seen in the winter period to the resident and migratory categories, with sufficient certainty, thereby increasing the sample size for other tests.

Consistency of migratory tendency

The 18 individuals that were observed in more than one winter were all consistent in migratory behaviour (10 residents and 8 migrants) and each was seen in the same specific location (Iceland or western Europe) in both winters. Where feather samples were taken in more than one year, there was no evidence of any bird changing its habitat or diet.

Factors influencing individual migratory programmes

Females and males were equally likely to migrate and there was no evidence that bigger (or smaller) birds were more likely to leave Iceland. Most Oystercatchers that winter in Iceland are in flocks in the west of the country, where the coast is warmed by the Gulf Stream. Unsurprisingly, westerly breeders were more likely to be resident than those in the south or northeast of Iceland (see figure below).

blog pie charts

Assortative mating

Vero and her colleagues were able to assign the migratory strategy to both members of the pair for 162 pairs (either by resightings or using predictions from isotopic signatures). Among these, 75 pairs (46%) were both migrants, 32 pairs (20%) were both residents and 55 pairs (34%) were mixed. The frequency of full-migrant, full-resident or mixed pairs varied significantly among regions, which was to be expected, given the differences in the likelihood of migrating from different parts of Iceland. There was no evidence of assortative mating; the likelihood of a particular individual pairing up with a migrant was as expected from the proportion of migrants in the area; it was not influenced by whether the particular individual was itself a migrant (see figure above).

To migrate or remain in Iceland

The consistency of adult migratory behaviour suggests that migratory strategy is determined in early life, and the regional variation in the frequency of migrants and residents may thus reflect variation in the conditions encountered by individuals during this life stage. As noted above, the frequency of residency is greatest amongst Oystercatchers breeding in the west of Iceland, which are the areas closest to the main wintering locations. Juveniles from the northwest and west are more likely to encounter these flocks of adult and sub-adult birds when moving south, than juveniles from the south, north-east and east, which are more likely to encounter migrating adults.

blog gen chThe regional variation in migratory strategy could arise through the influence of social cues, with juveniles adopting the behaviour of Oystercatchers they encounter and then recruiting back into their natal locations (more about this in Generational Change, focusing on Black-tailed Godwits). Birdwatchers across Europe will hopefully help to test this theory, by tracking colour-ringed juveniles during the early years of life. This is all part of a quest to identify the conditions that influence migratory behaviour and to understand the consequences, in terms of survival rates and productivity, of adopting different migratory traits.

Paper

Please click on the title below to access the paper:

Individual variation in migratory behavior in a sub-arctic partial migrant shorebird by Méndez V., Alves J.A., Þórisson, B., Marca, A., Gunnarsson, T.G., Gill, J.A.  Published in Behavioral Ecology (2020).  doi.org/10.1093/beheco/araa010 

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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

 

Fennoscandian wader factory

 

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Nesting Temminck’s Stint – the smallest of the 22 wader species for which trends are reported

At the end of the summer, vast numbers of waders leave Norway, Sweden and Finland, heading southwest, south and south-east for the winter. In a 2019 paper by Lindström et al, we learn what is happening to these populations of Fennoscandian breeding species, as diverse as Temminck’s Stint and Curlew. The news for the period 2006 through to 2018 is basically pretty good – most populations have been stable and there are even some that have increased – but there are worrying signs for Broad-billed Sandpiper, Red-necked Phalarope and Whimbrel.

Breeding waders of Fennoscandia

blog mapAs a volunteer taking part in the Breeding Bird Survey (BTO/JNCC/RSPB) in the UK, I feel that I do my bit to monitor what is happening to local bird population – providing counts that build into national trends. The work involved in delivering indices for breeding waders across the area of Fennoscandia shown in the map is in a different league. Here, counters visit habitats as diverse as forests, wetlands, mires and tundra, within the boreal and arctic areas of Norway, Sweden and Finland. Some survey sites are so remote that access requires the use of helicopters.

Fennoscandia provides important breeding areas for a large set of wader species, and models suggest that these habitats may be particularly vulnerable to climate change, especially increasing summer temperatures. The 2006-18 analysis in Wader Study, the journal of the International Wader Study Group, presents population trends for 22 wader species. The trends are based on 1,505 unique routes (6–8 km long), distributed over an area that’s about four times that of the United Kingdom. 

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The surveys took place across the whole of Norway and Finland, and in the northern two thirds of Sweden, between 58°N and 71°N, which largely coincides with the boreal, montane and arctic regions of Fennoscandia. The systematic distribution of these routes ensures that the main habitats in these countries are sampled in proportion to the area they cover. The paper describes the methodologies used in the three countries and the way that data were combined, especially factors used to translate sightings of individuals into ‘pair-equivalents’.

Overview of results

blog mountainLooking at the results from across Norway, Sweden & Finland:

  • In terms of pure numbers, Golden Plover was the most commonly encountered wader species, followed by Wood Sandpiper, Snipe, Greenshank and Green Sandpiper.
  • The five most widespread species, seen on the highest number of routes, were Snipe, Green Sandpiper, Greenshank, Wood Sandpiper and Common Sandpiper.
  • Wader species richness and the total number of wader pairs were both higher with increasing latitude; the median number of wader pairs per 10 km increased from just below 3 at latitudes 58–60°N, to just above 26 at latitudes 69–71°N.
  • Using a multi-species indicator, the research team found no general change in wader numbers over the period 2006-18.
  • The trends were significantly negative for three species: Red-necked Phalarope (-7.9% per year), Broad-billed Sandpiper (-5.4% per year) and Whimbrel (-1.3% per year).
  • The trends were significantly positive for three species: Oystercatcher (+4.9% per year), Dunlin (+4.2% per year) and Wood Sandpiper (+0.8% per year).
  • There was no significant trend for another 16 species for which encounters were deemed to be frequent enough for analysis.
  • Population trends of long-distance migrants tended to be more negative than those of medium-distance migrants. This is discussed in detail in the paper.

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Focusing on some key species

The Lindström et al paper is a tremendously rich source of information and references. Here are some species-specific highlights.

Oystercatcher. In the context of a species that is declining across NW Europe, the fact that there is a significant increase in Oystercatchers across Fennoscandia may be surprising. However, the authors note that there was a jump in numbers between 2006 and 2007 with little change since then.

blog l graphLapwing. The trends within the three Fennoscandian countries are very different. In Norway, there has been a dramatic decline (-15.2% per year during 2006–2018) and the Lapwing is now nearly extinct in many areas. The trend in Sweden is also significantly negative (-5.8% per year). In Finland, however, where the species is more widespread and numerous, there has been a strong increase (+5.9% per year) during the same period. See figure alongside.

Golden Plover. No significant change overall. There are some country-specific differences in trends, with a moderate decline in Norway being countered by a moderate increase in Sweden. 

Snipe. The overall trend of this species for each country indicates an initial decline followed by an increase. A similar pattern has been noted in the UK’s Breeding Bird Survey over the same period. 

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Nesting Whimbrel

Woodcock. The trend for 2006–2018 is basically stable and similar in all three countries.

Curlew. There is no significant trend, overall, but populations in Norway and Sweden have declined at the same time that numbers in Finland have increased.

Whimbrel. Fennoscandian trend indicates a decline of 1.3 % per year. Whimbrel is doing poorly in Norway and Sweden but better in Finland. 

Wood Sandpiper. This widespread species has increased slowly (0.8% per year), a trend that is largely driven by Norwegian and Swedish populations.

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Wood Sandpiper was the second most commonly encountered wader

Redshank. The fact that no change was discernible, suggests that boreal and arctic populations are faring much better than the breeding populations further south in Europe. For example, see Redshank – warden of the marsh.

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Redshank – more obvious than most breeding waders encountered!

Spotted Redshank. The estimated annual decline for Spotted Redshank is 2.8% per year but the species is too thinly spread for this to provide significant evidence of a decline. This rate is very similar to the recent drop in the Wetland Bird Survey index in the UK. See Fewer Spotted Redshanks.

Broad-billed Sandpiper. This species has the second most negative trend among the 22 species analysed (-5.6% per year). The bulk of information comes from Finland where the trend is even more negative (-7.5% per year). Birds head southeast in the autumn to countries bordering the Indian Ocean – areas for which winter trend data are not available. The species is still considered to be of ‘least concern’ but perhaps this designation may need to be revisited?

Dunlin. Breeding birds in the survey area are largely of the alpina race. The overall trend is significantly positive (+4.1% per year), which is in sharp contrast to the strong declines of the schinzii subspecies that breeds around the Baltic Sea, western Finland and further south and west in Europe.

blog rnpRuff. There were major declines in the period immediately prior to this review (Lindström et al. 2015) but changes reported here are lower (-2.3% per year) and the decline is not statistically significant.

Red-necked Phalarope. The authors write, “This species has the most negative trend of all the 22 species [-7.9% per year], with most data coming from Sweden. We do not know the cause of this decline but, given that this species shares its south-eastern migration route with Broad-billed Sandpiper, whose population exhibits the second largest decline, the relevant problems might largely apply somewhere along the migration routes”.

Link to Britain & Ireland

As shown in Which wader when and why? there are strong migratory connections between Fennoscandia and the British Isles. Some waders, such as Green, Common and Wood Sandpipers, pass through on their way south in the autumn, whilst many more fly here for the winter, to take advantage of the warmer maritime climate.

Three wader species with particularly strong links between Fennoscandia and Britain & Ireland are still shot and eaten in these islands. Each autumn, large numbers of Woodcock, Golden Plover and Snipe cross the North Sea. It is difficult to ascertain figures for the number that are shot but there is agreement that the vast majority are winter visitors, as opposed to native birds. The results presented in the paper suggest that there have been no discernible changes in the Fennoscandian populations of these three game species in the period 2006-18. Two earlier WaderTales blogs focus on Woodcock and Snipe in Britain & Ireland:

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There has been no significant change in Golden Plover numbers across Fennoscandia

Two WaderTales blogs about wintering waders in Great Britain and the island of Ireland were published in 2019, based on reviews in British Birds and Irish Birds. These were Do population estimates matter? and Ireland’s wintering waders. The six big losers, in terms of wintering numbers in these islands, were Knot, Oystercatcher, Redshank, Curlew, Grey Plover and Dunlin. Knot arrive from Greenland and Canada, with Grey Plover flying from Russia, but it is interesting to think about this Fennoscandian breeding analysis in the context of winter losses of the other four species.

  • Wintering numbers of Oystercatchers have dropped recently in Britain and in Ireland. The population is made up of migrants from Iceland (more about this here), very large numbers from Norway, birds that stay within the British Isles and smaller numbers from other European and Scandinavian countries. Given there is no discernible decline in Fennoscandia, it seems likely that much of the decline can be attributed to a major fall in Scottish breeding numbers (more about this here).
  • Most Redshank wintering in Britain & Ireland are of local or Icelandic origin. Fennoscandian numbers seem to be stable; if there were any changes, these would probably not be apparent in wintering numbers within the British Isles.
  • The Eurasian Curlew has been classified as ‘near-threatened’ and the species is known to be declining in many areas (see this blog about serious problems in Ireland). Ringing shows a particularly strong link between Finland, where breeding numbers seem to be increasing, and Britain & Ireland. The decline in British and Irish winter numbers is probably being driven by lower breeding numbers within the British Isles and in countries such as Sweden, Norway and Poland.
  • There is a theory that new generations of alpina Dunlin may be more likely to winter within Europe’s mainland estuaries, instead of continuing their westward migration across the North Sea. This might explain the apparent anomaly between the 4.1% per annum rise in Fennoscandian numbers and recent winter declines of 3% in Britain and over 20% in Ireland.

Going forwards

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Some of the survey areas were in particularly remote areas

Many of the study squares that were covered during these surveys are a long way from the main centres of human population in Norway, Sweden and Finland. The governments of the three countries are to be congratulated for supporting this important monitoring, which relied on the commitment of hundreds of volunteers. It is to be hoped that these surveys will continue and that further species-focused work will be able to explain some of the differences across Fennoscandia, particularly between eastern and western areas. The rapid declines in numbers of two species that migrate southeast each autumn (Broad-billed Sandpiper and Red-necked Phalarope) highlights the need for better information about what is happening on the flyway linking Fennoscandia with the Arabian Sea and coastal countries of the Indian Ocean.

Paper

Population trends of waders on their boreal and arctic breeding grounds in northern Europe: Åke Lindström, Martin Green, Magne Husby, John Atle Kålås, Aleksi Lehikoinen & Martin Stjernman. Wader Study 26(3)

Click on the title of paper to access it on the International Wader Study Group website. Paper is only available to members of IWSG. If you have read the whole of this blog you’ll probably want to join!

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Nesting Bar-tailed Godwit in smart summer plumage


GFA in Iceland

Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

 

 

Sixty years of Wash waders

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Weighing a Turnstone

The Wash Wader Ringing Group (WWRG) started with a bang on 18 August 1959, when the team made a catch of 1,132 birds in a Wildfowl Trust rocket-net at Terrington, in Norfolk. Over the years, cannon have replaced rockets, catches have become generally smaller and the scientific priorities have been refined, but the Group continues to focus upon discovering more about the waders that use the Wash. This blog attempts to summarises what has been learnt about the waders that rely upon the Wash, the vast muddy estuary that lies between Lincolnshire and Norfolk, on the east coast of England.

Wee quiz: What’s the best match between these Wash waders and the countries that they are quite likely to have come from? Answers at the end of the blog:

  • Species: Bar-tailed Godwit, Black-tailed Godwit, Curlew, Oystercatcher, Sanderling & Turnstone
  • Countries: Canada, Finland, Greenland, Iceland, Norway & Russia

Sixty years ago, the first goal was to understand where the vast flocks of waders that visit the Wash came from – a task that would provide great insights into the way that the whole East Atlantic Flyway works. In this time, over 300,000 birds have been caught and ringed on the Wash, as you can see in the table below. Equally importantly, hundreds of bird-ringers from across the UK and scores of visitors from around the world have joined WWRG teams, in order to learn more about the study of shorebirds. Further international collaboration has been fostered through overseas visits by WWRG members and emigration of some key personnel. The impact of the Group is truly global, as you can read in the WWRG report for 2014/2015.

wwrg table

A total of 307,226 birds is impressive, especially when some of the species totals are compared to the national totals of the BTO Ringing Scheme for the whole of Britain & Ireland since 1909. WWRG is responsible for over 40% of the Grey Plover, Knot, Sanderling and Bar-tailed Godwit, with Grey Plover topping the list at nearly 60%. These are terrific achievements for a group of volunteers. I don’t have the figures but I reckon that Nigel Clark has been responsible for the largest number of catches.

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Firing box connected to 4 cannon-nets

In the early days, rocket nets were borrowed from the Wildfowl Trust for an annual summer week of catches, but the development of cannon-nets gave opportunities for all-year ringing. The intensity of the Group’s activities grew in the 1970s, when there was a threat to build a freshwater reservoir on the mudflats. For a couple of years, Clive Minton (founder and leader) persuaded us to visit fortnightly, so that we could get better data on weight-gain and turn-over, using a mixture of cannon-netting and mist-netting. Everything we knew was published by the Group as The Wash Feasibility Study in 1975. These days, the Group gets together about ten times a year for catching and colour-ring-reading sessions.

wwrg oldies

By catching and ringing large numbers of the key species that visit the Wash, the Group was able to generate maps showing what are now well-known patterns of migration (see Which wader, when and why?). Early on in the Group’s history, there was a focus on nine species, with Black-tailed Godwit added as a tenth when numbers increased. Each of these species has its own section below. The maps were prepared for the Wash Wader Ringing Group 2016/2017 Report by Ryan Burrell, using data stored within the BTO archives. Blue dots represent WWRG-ringed birds that have been found abroad. Red triangles represent foreign-ringed birds caught on the Wash. The base maps used are by courtesy of Natural Earth (www.naturalearthdata.com).

Oystercatcher

wwrg map OCThe map alongside clearly demonstrates the strong link between the Wash and Norway. Other interesting things that have been discovered about Oystercatchers:

  • They live a long time. An Oystercatcher that we caught at Friskney on 30 July 1976 broke the longevity record for a BTO-ringed wader when it was shot in France on 4 April 2017 (41 years 1 month and 5 days). It was ringed as an adult so we don’t know the exact age – but it must have been at least 43 years old. There’s a WaderTales blog with a list of longevity records for BTO-ringed waders.
  • When life gets tough, Oystercatchers fail to complete their autumn moult, retaining some of their outer primaries for an extra year. The ability to complete moult and annual survival rates are both affected by cockle and mussel supplies on the Wash. There’s more about this in two papers in Biological Conservation and the Journal of Applied Ecology.

Grey Plover

wwrg GV GVIn the early days of the WWRG, Grey Plovers occurred in much smaller numbers than they do now. Writing in an article about the first 40 years of the Group, Clive Minton told the story of the first catch of 100, made in 1963, that was celebrated with three bottles of champagne provided by the late Hugh Boyd, delivering on an incentive that he had promised.

  • Over half of the Grey Plover that have been ringed in Britain & Ireland since 1909 have been ringed by WWRG since 1959 (58.9%)
  • All of the Grey Plover using the Wash breed in Siberia. Some birds spend the winter on the Wash but there are autumn moulting flocks of birds that will go on to winter in other parts of Britain & Ireland, and spring and autumn passage of birds that travel as far south as West Africa.
  • Grey Plover are late to leave the Wash, with the last departures not occurring until the start of June. Unsurprisingly, they are some of the last waders to return at the end of summer, which puts pressure on birds to finish moult before the short, cold days of winter. Some adults fail to complete primary moult, especially if food supplies are low. There is more about Grey Plover moult in this WaderTales blog.

wwrg map GV KN

Knot

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First-winter Knot (subterminal bands on wing coverts and, as yet, unmoulted juvenile fethers on upper-parts)

Knot (or Red Knot) are truly international waders, as is shown in this map of movements of islandica  (and a few canutus) birds  to and from the Wash. Several WWRG members have been heavily involved in efforts to understand the decline in numbers of the rufa subspecies in Delaware Bay (on the North American eastern seaboard) and Clive Minton has been at the heart of efforts to explain the sudden drop in survival of piersmai and rogersi adults that winter in Australia and migrate to Arctic Russia via the Yellow Sea (see Wader declines in the shrinking Yellow Sea).

  • We are still learning about Knot migration. The cluster of reports of WWRG-ringed birds in Northern Norway looks odd on this map projection but it turns out that this is a well-used stopping-off point for islandica Knot heading for northern Greenland and NE Canada. This route was first confirmed in 1985, when a joint Durham University and Tromsø University expedition caught 18 Wash-ringed birds in a total catch of 1703 birds.
  • The dot in Siberia looks odd but isn’t. This will be a bird of the canutus race, small numbers of which pause on the Wash in autumn and spring, on their way between the Russian Arctic and west Africa.
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    Setting cannon-nets

    Many birdwatchers visit the Wash in autumn and winter to see the swirling Knot flocks at Snettisham and Holme. If high tide is at first light, Knot and other waders sometimes roost on Heacham Beach, giving the occasional opportunity to make a significant catch. The most recent of these, on 11 February in 2012, included 2757 Knot, 77 of which were already wearing rings.

  • Knot numbers on the Wash are highest in autumn. After moulting, many birds fly west. Colour-flagging by WWRG is designed better to understand these movements.
  • The most recent analysis of wader populations in Great Britain showed that there was a drop of nearly 20% in wintering Knot numbers (from 320k to 260k) in less than a decade (see Do population estimates matter?). Regular catches on the Wash will help produce estimates of annual survival rates and age ratios of the islandica subspecies.

Sanderling

wwrg sanderlingThe biggest catches of Sanderling are generally in the summer, when the Wash is a meeting point for birds from Greenland and Siberia. July can sometimes see catches of 200 or more birds. Traditionally, a Sanderling catch was the curtain-raiser at the start of Wash Week, an opportunity for the whole team to make one catch before splitting into ‘Terrington’ and ‘Lincolnshire’ teams for the rest of the main summer trip.

  • Wintering Sanderling on the Wash are thought to be exclusively of the race that heads northwest in the spring, to Greenland via Iceland.
  • Late summer and spring see the addition of birds passing through on their way from/to Siberia and extra birds from Greenlandic breeding areas.
  • I well remember the first time we caught a Sanderling (on 26 July 1975) wearing an Italian ring (caught in Italy 9 May 1975). Thanks to Jeroen Reneerkens (whose work is covered in this blog) I now understand that this is probably a bird that migrates from Namibia to Greenland in spring, via the Mediterranean. It will have been on its way back to Namibia when caught in July.

wwrg map SS DN

Dunlin

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Sam Franks, looking for the buffy tips on inner coverts, which distinguish first-year birds from adults

Nearly half of the waders caught by WWRG have been Dunlin – a total of 140,168 up until the end of 2018. There were really big flocks of Dunlin in the 1970s but numbers have dropped over the years, with peak counts now half what they were, according to WeBS data.

  • We caught over 3,500 Dunlin in one week in 1976 but the annual total has exceeded 1,000 in only four of the last ten years. Partly, this reflects a change in behaviour in the summertime, with fewer waders roosting on fields and hence less catchable.
  • Three races of Dunlin visit the UK. Our winter birds are alpina, from Siberia, NW Russia and northern Scandinavia. A lot of July birds are schinzii, breeding in the UK and as far north as Greenland, and we occasionally try to convince ourselves that we have caught an arctica from northern Greenland.
  • Data collected for the WeBS survey suggest that national winter totals have dropped by over 40% in 25 years. This could perhaps partly be explained by a redistribution of alpina, with new generations of young birds settling in wintering areas on the other side of the North Sea. Warmer winters may well make this a more practical proposition than in the 1970s. There’s more about this in this paper.

Black-tailed Godwit

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Newly ringed Black-tailed Godwit, caught in a mist-net at night.

Black-tailed Godwits became a priority species in 1995, when Jennifer Gill (University of East Anglia) started a project to study the movements of individuals, using colour-rings. Nearly 25 years later, the WWRG-ringed Black-tailed Godwits have contributed data to numerous papers, largely focusing upon migration.

  • The Wash is a hugely important area for moulting islandica Black-tailed Godwits. Some birds stay in East Anglia for the winter but others move south and west within the UK, west to Ireland and south to France, Portugal and Spain.
  • There are several blogs about Black-tailed Godwits in this WaderTales contents list.

Bar-tailed Godwit

One of the key things that was learned from the sudden decline in annual survival rates in a range of species that use the Yellow Sea (as mentioned above) is a need for regular monitoring of marked birds. The WWRG’s Scientific Committee set up colour-flagging projects for Bar-tailed Godwit, Curlew and Grey Plover, in order to increase the reliability of estimates of annual survival for three species that the Group does not catch in sufficient numbers to generate good retrap histories. Birdwatchers can help by reporting colour-marked birds here.

wwrg barwit map etc

  • In Bar-tailed Godwits: Migration & Survival there is a comparison of the data generated by a catch of 505 Bar-tailed Godwits in 1976 with the information that has been generated recently, using colour-flags.
  • Bar-tailed Godwits are long-lived birds. A WWRG bird holds the current record for a BTO-ringed Bar-tailed Godwit: 33 years and 11 months between ringing in 1978 and recapture in 2008. BTO longevity records are discussed in this WaderTales blog.
  • Colour-ring reading is now a significant element of Group activities, as described by Rob Pell in the WWRG Report for 2016/2017.

Curlew

Back in the 1970s, Curlew were still hunted on the Wash (paté made from autumn-shot birds was reported to be very tasty). Shooting stopped in Great Britain in 1981, when the maximum winter count on the Wash had dropped to about 3,000 birds, and by 2003/04 the maximum winter count was 15,336. Since then, numbers have declined, in line with national and international trends.

wwrg curlew map etc

  • A large number of Curlew on the Wash in winter are from Finland and surrounding countries. Surprisingly few are of UK origin.
  • Birds wearing WWRG leg-flags have been observed breeding in the Brecks (Norfolk/Suffolk).
  • The Curlew is internationally designated as ‘Near Threatened’. Is this really true when we can still see a field with 1000 roosting Curlew in Norfolk? Answers here.

Redshank

wash redshThe latest population estimates suggest that Great Britain has lost 26,000 wintering Redshank in less than a decade, representing a drop of 20%. Perhaps WWRG data can be used to help to explain these declines? Here are some of the things we know:

  • The Redshank on The Wash in the winter are mainly a mixture of birds from around the Wash, across the UK and from Iceland.
  • In cold winters, Redshank wintering on the Wash die in large numbers. After a period of severe weather in 1991, nearly 3,000 wader corpses were collected from along the tide-line, about 50% of which were Redshank. The winter WeBS counts for Redshank dropped by 50% after this mortality event but have recovered somewhat since then.
  • An analysis of nearly 1,000 dead Redshank showed that about two-thirds were of Icelandic origin. There was a tendency for smaller birds to be more susceptible to cold weather mortality than larger birds of the same species (More information in this paper by Jacquie Clark)

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Turnstone

wash ttWinter Turnstone are birds that will head for Greenland and NE Canada in the spring but recoveries of birds in Finland and other Scandinavian countries indicate a passage of continental birds. African recoveries of WWRG-ringed birds probably include birds from Canada/Greenland and Finland/Scandinavia.

  • Turnstone wearing US Fish & Wildlife Service rings are occasionally caught on the Wash. Some of these rings were put on by Guy Morrison and his colleagues in Alert, Ellesmere Island, Canada. Guy was an early member of WWRG. It’s a small world!
  • The first Wash Turnstone were colour-ringed in 1999, as part of a study to understand why birds were feeding on the docks at Sutton Bridge. There is a WaderTales blog about the resulting paper by Jen Smart and Jennifer Gill. Colour-ringing continues, to measure annual survival rates.
  • Turnstone have a reputation for eating almost anything (including dog excrement and a human corpse) so do not be surprised if you see a colour-ringed bird scavenging for chips on the Hunstanton sea-front.

A few more highlights

Ringed Plover: this is not one of the ten key study species but 1,432 have been ringed between 1959 and 2018. Some birds are local breeders that hardly move anywhere but other birds link the Wash with Greenland, northern Norway, Morocco and Senegal.

wwrg GKGreenshank: The Group supports a colour-ringing project that was initiated by Pete Potts, in Hampshire. More information here.

Spotted Redshank: During the period 1959 to 2018, WWRG ringed a total of 85 Spotted Redshank, representing over 20% of the total ringed in Britain and Ireland since 1909. Amazingly, sixty of these birds were ringed on the same day – 27 July 1975. There is a blog about this catch and the recent decline in the number of Spotted Redshank visiting the UK. Fewer Spotted Redshanks.

Ruff: Until its closure, WWRG members spent many a smelly night at Wisbech Sewage Farm. This was a great place to catch Ruff, Curlew Sandpipers, Green Sandpipers etc. in mist-nets. Group members wrote a paper about Ruff moult and migration.

Rares: Occasionally there are surprises! WWRG has caught one each of Stone Curlew, Pectoral Sandpiper, Broad-billed Sandpiper and Terek Sandpiper. The last bird features in this WWRG blog.

What do we know now?

Migration studies have revealed the importance of the Wash to half a million or more waders each year – birds that spend the whole winter, others that refuel in the spring and vast numbers that rely on the food supplies in the mud to provide the energy for the post-breeding moult. There’s a selection of papers that have included WWRG data here, on the Group’s web-site.

wwrg cr TTThe Group still aims to maintain its general ringing programme, so that a representative sample of the key species carry rings. Colour-ringing projects aim to provide survival estimates for Curlew, Bar-tailed Godwit, Grey Plover and Turnstone, with Greenshank and Black-tailed Godwit colour-rings contributing to migration studies. Birdwatchers who visit the Wash can help by reporting colour-marked birds here, on the WWRG web-site.

WWRG data have been used to help inform decisions about the future of the Wash but the threats keep coming. Studies of migration and seasonal turn-over in numbers contributed hugely to decisions to provide national and international protection to the area and to fend off the 1970s plan to build a freshwater reservoir on the rich mudflats. The information that has been generated by many generations of volunteers over a period of sixty years has been used to manage the level of shellfish exploitation, to inform decisions about wind turbine locations and to manage activities that can cause disturbance.

The Wash Wader Ringing Group is very keen for its data to be used – and not just for impact assessment studies. Click here to learn more.

Diamond Jubilee

PLI

Phil Ireland releasing a Curlew

Over one thousand people are estimated to have contributed to sixty years of the Wash Wader Ringing Group’s activities. We have lived in barns, rolled cars, dug tens of thousands of holes, carried nets for miles, made important catches, had depressing failures, got frostbite, been threatened by surge tides and made friends for life.

In the whole of this period, there have been only two leaders of the Group – Clive Minton* (1959-1981) and Phil Ireland (1981-present). Bird ringers, wader biologists and millions of waders owe them both a huge debt of gratitude.

You can read more about the history of WWRG on the Group’s website:

*Clive Minton died in a car crash a few months after this blog was written. Friends and colleagues have shared some wonderful memories on the IWSG website.

wwrg sunset

Photo at the top of this blog is by Cathy Ryden. Many thanks to her and to other photographers.

Wee quiz:

  • Bar-tailed Godwit – Russia
  • Black-tailed Godwit – Iceland
  • Curlew – Finland
  • Oystercatcher – Norway
  • Sanderling – Greenland
  • Turnstone – Canada

GFA in Iceland

Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

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Ireland’s wintering waders

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There’s still space for a few Knot

The island of Ireland is a great refuge for wintering waders, washed as it is by the warm waters of the Gulf Stream. It’s just a quick hop across the Atlantic from Iceland for Black-tailed Godwits, Golden Plovers, Redshanks and Oystercatchers. For birds travelling from Siberia, such as Dunlin and Grey Plovers, it’s a longer journey but one that’s well worth making.

If Ireland is such a great destination for shorebirds, why do the latest population estimates reveal a decline of nearly 20% in wader numbers in just five years?

This blog summarises the wader information, published in Estimates of waterbird numbers wintering in Ireland, 2011/12 – 2015/16 in Irish Birds. The totals in the report are split into counts for the Republic of Ireland and Northern Ireland but, given that waders don’t recognise borders, most of the comments in this blog relate to the whole of Ireland. The results for 2011-16 have been compared to the equivalent figures for 2006-11 and set in the context of the totals of wintering waders throughout the East Atlantic flyway, as combined by Wetlands International. The Irish data were collected by the amazing volunteers who make monthly, winter counts for I-WeBS (BirdWatch Ireland & National Parks & Wildlife Service) and WeBS (BTO/RSPB/JNCC in Northern Ireland).

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Headline figures

Fifteen species are considered in this report. The most numerous are Lapwing and Golden Plover, which account for an estimate over 170,000 individuals between them, whilst the smallest contributions are made by Purple Sandpiper (662) and Greenshank (1317). In total, the average estimated number of waders in the winters during the period 2011-16 is 429,170 birds but it should be noted that this total excludes two widespread and common species – Woodcock and Snipe – as well as the enigmatic Jack Snipe. To update previous estimates for these three species, which were last made using distribution and abundance data collected during Bird Atlas 2007-11 fieldwork, it would be necessary to run a special inland survey. There is also some question about Lapwing and Golden Plover numbers, simply because so many of these birds are found in areas that are not covered by monthly waterbird counts.

Biggest changes

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The Irish Sanderling population has increased by 13.2% in five years

The combined average winter maximum count of the 15 wader species examined in the report declined by 102,310 birds (19%) in the five-year period between 2006-11 and 2011-16. This is extremely worrying. If Lapwing and Golden Plover are excluded from consideration, as there is uncertainty about the completeness of counts, there are five species that are of particular concern; Knot numbers dropped by more than 40% and Oystercatcher, Dunlin, Redshank and Turnstone numbers by more than 20%. The Purple Sandpiper population estimate dropped by over 30% but relatively small numbers of this species are encountered around the rocky coast of Ireland. The only species to show increases were Sanderling, Bar-tailed Godwit, Black-tailed Godwit and Greenshank.

In a previous WaderTales blog, there is detailed information about population estimates for Great Britain: Do population estimates matter? In Great Britain there were similar rates of decline for Redshank and Turnstone (measured over an eight-year, rather than five-year period) but much smaller falls for Knot, Oystercatcher and Dunlin. The possible causes of the changes in Ireland are discussed in the paper in Irish Birds. They include flyway-scale declines (e.g. Knot and Curlew) and the possibility that more birds from the east are now wintering on the coasts of mainland Europe (e.g. Dunlin and Grey Plover).

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European context

Blog tableThe table alongside gives an indication of the relative importance of Ireland, Great Britain and, together, the British Isles to the birds that use the East Atlantic flyway during the winter period. The three columns show the percentage of each species found in each of the three regions. Summarised international counts, as used in the paper, were kindly provided by Wetlands International. In the case of four species, Ireland is host to a significant proportion of the Icelandic breeding population (Oystercatcher, Golden Plover, Black-tailed Godwit and Redshank). There’s a WaderTales blog about the close link between Ireland & Iceland. Another blog – Which, wader, when & why? – summarises migration to, from and through Britain & Ireland.

Notes: As mentioned earlier, there are questions about the precision of estimates for Lapwing and Golden Plover, although the population trends are reliable. The Ringed Plover percentage seems high (98% for British Isles) but this may well reflect the fact that the Non-estuarine Waterbird Survey has uncovered significant numbers of the species on the open shores of Great Britain. These extra birds are included in the new totals for GB but not in the flyway total. The percentages for Black-tailed Godwit seem low, as discussed further down.

Ireland is particularly important for Golden Plover, Ringed Plover, Bar-tailed Godwit and Black-tailed Godwit, as well as for the Icelandic subspecies of Redshank. Greenshank is excluded because the percentages are below 1% of the flyway population for Ireland and for Great Britain.

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11% of Bar-tailed Godwit on the East Atlantic Flyway spend the winter in Ireland

Although there are important populations of breeding waders in Ireland, the shores and wet fields of the island really come into their own during July and August, when the first ‘winter’ waders arrive, and they only become quiet again in April and May, when the last birds head north and east to nest. A successful breeder is likely only to be away for four or five months, meaning that these waders will spend by far the largest part of the year in Ireland. The island is even more important for immature birds. Young Oystercatchers that arrive from Iceland, Scotland or perhaps Norway when just a few months old are likely to spend the next 30 months in Ireland before making their first trip north. There is a WaderTales migration blog about the Oystercatchers that fly from Iceland: Migratory decisions for Icelandic Oystercatchers.

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Curlew in the Republic

Curlew numbers in the Republic of Ireland illustrate the relative importance of the country for breeding and non-breeding populations. The winter population estimate for Curlew in the Republic is 28,300 but the most recent survey conducted by BirdWatch Ireland and NPWS, as summarised in the WaderTales blog Ireland’s Curlew Crisis, reveals that the number of breeding birds has crashed to just 138 pairs. Accounting for young Irish birds that have not started to breed, and even if we assume that all Irish birds stay in the country for the winter, then the total number of home-grown Curlew seen in non-breeding flocks is at most about 400. This means that every winter flock of 70 Curlew will contain an average of just one Irish bird. Far more deliver their curl-ew calls with a Scottish, Finnish or Swedish ‘accent’. The map below shows the migration pattern for Curlew ringed in or found in Britain & Ireland.

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Black-tailed Godwit

In the table above, it looks as if 18% of Iceland’s Black-tailed Godwits spend the winter in Ireland. This is probably an underestimate of the importance of the Republic of Ireland and Northern Ireland to the species. The flyway total for Black-tailed Godwit is given as between 98,000 and 134,000 in the Irish Birds paper and the percentage figure is based on 110,000. These three figures are almost certainly too high, as they build upon country-based estimates that have subsequently been revised. The true figure is likely to be around 60,000 to 65,000 (J. Gill pers. comm.), which would suggest that the maximum winter count in Ireland of 19,800 represents at least 30% of the islandica Black-tailed Godwits. Add in extra birds that moult in Ireland in the autumn, before moving further south to countries such as Portugal, and other birds that spend spring months on the island, and Ireland becomes even more important for Black-tailed Godwits!

blog BTMost birdwatchers might associate flocks of waders with estuaries but Black-tailed Godwit is an excellent example of a species that also relies on inland fields, either close to estuaries or along river valleys. Whilst undertaking PhD research on Black-tailed Godwits in south-east Ireland, Daniel Hayhow showed that there is insufficient time to find enough estuarine food during the mid-winter tidal cycles, with birds topping up their resources on grassland. You can read more about the energetic consequences of choosing to winter in eastern England, Portugal and Ireland in this blog: Overtaking on migration. Site designation and planning decisions need to take account of the grassland feeding requirements of Black-tailed Godwits and other waders that do not spend all of their time on estuaries, particularly Curlew.

Conservation implications

Some of the issues facing waders may be related to threats that species face in the breeding grounds. However, it may be easier to introduce measures that provide better protection and feeding opportunities in the wintering area, as ways of maintaining populations through the non-breeding season, than it is to deal with problems in the High Arctic. (Although we can all help by reducing carbon emissions, in order to minimise global warming, of course).

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Reading the report, I was reminded of the need to consider a range of conservation issues:

  • Care needs to be taken when considering shoreline developments. These can directly remove habitat or squeeze the width of the intertidal zone.
  • Increased harvesting of shellfish can affect species such as Oystercatcher and Knot and brings risks of introducing alien species and diseases.
  • In the drive to cut carbon emissions, tidal, wave and wind power developments need to be sited in appropriate places.
  • Off-shore harvesting of growing kelp beds has been suggested, as a way of producing fertiliser and biofuels. This process could reduce protection for beaches and change the availability of resources for species such as Turnstone and Sanderling.
  • Grassland areas need to be considered (and not just estuaries) when planning protection for species such as Curlew and Black-tailed Godwit.

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Estimates of waterbird numbers wintering in Ireland, 2011/12 – 2015/16. Brian Burke, Lesley J. Lewis, Niamh Fitzgerald, Teresa Frost, Graham Austin, and T. David Tierney. Irish Birds No. 41, 1-12.

There is a complementary paper in British Birds, covering Great Britain. The wader information is summarised in this blog: Do population estimates matter?


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