In amongst the tidewrack

Double-banded Plover

Tidewrack has an image problem. Who wants to see a dark line of seaweed on a beach of white sand or to smell rotting beds of kelp in enclosed bays? Shorebird conservationists may understand the feeding opportunities that are provided by fresh and older seaweed but, for tourist boards, tidewrack is something that needs to be cleared away.

It turns out that tidewrack is not just a biodiverse habitat; the mere presence of seaweed creates spaces in which waders can roost and find shelter. In a paper in the Journal of Applied Ecology, Timothy Davis & Gunnar Keppel get down to Turnstone-level, to investigate the important microhabitats within different forms of beach-cast wrack.

An Australian autumn

Readers in the northern hemisphere may well have seen wintering waders sheltering in the lee of clumps of tidewrack, as a gale blows snow and sand across a beach. At Danger Point, about half-way between Melbourne and Adelaide on the coast of Australia, conditions are somewhat different, with December and January temperatures topping 30°C, conditions in which waders must try to avoid over-heating. By April, when the Davis & Keppel study was carried out, conditions were autumnal, with cool mornings. Three of the species that might be seen on a European beach were present – Turnstone, Sanderling and Bar-tailed Godwit – but with the addition of Curlew Sandpipers and Red-necked Stints, that were about to depart for Siberia, and Double-banded Plovers that breed in New Zealand.

Which looks best – a barren beach or one strewn with seaweed?

What might waders be looking for?

Red-necked Stints

The research team was interested in the range of microclimates available on beaches with beach-cast wrack, to investigate the link between microclimates and microhabitats and how they are used  by waders. They expected to find warmer temperatures and higher humidity on aged wrack, due to advanced decomposition, and ameliorated conditions where wrack deposits provided shelter from prevailing winds. They predicted that waders would use microclimates that could reduce energy loss.

Observations

Data on temperature and humidity were collected by creating miniature Stevenson Screens – hollow white practice golf balls with iButtons inside them, attached to short bamboo canes, so as to be 10 cm above the substrate surface. If interested in conducting this sort of study, it would be sensible to read the methods section of the paper. Sample points were on bare sand, in areas with fresh wrack deposited on the sand and in beds of old tidewrack. Based on surrounding features and observations of prevailing winds, sample points were classified as sheltered or exposed.

Instantaneous scan sampling was used to classify migratory shorebird behaviour for the entire Danger Point study area (i.e., the area over which the microsensors were placed) at 15 min intervals on four days during April, as birds were preparing to migrate. Birds were classified as roosting (loafing, sleeping or preening) or as foraging on one of the three substrate types.

Variability of microclimate

As expected, there were significant differences among the three substrates (sand, fresh wrack and aged wrack) for mean, maximum and minimum temperature and absolute humidity. The temperature above the surface of aged wrack was consistently higher than elsewhere, with one notable exception: in the early mornings, when newly deposited seaweed retained some of the heat from the warmer ocean, temperatures were warmer on fresh wrack than on sand and aged wrack. For aged wrack, humidity was highest above deeper beds.

Curlew Sandpipers on the tide-edge

Bird Behaviour

Six species of wader were studied and included in ‘all waders’ counts but there were insufficient sightings of Bar-tailed Godwit, Curlew Sandpiper, Ruddy Turnstone and Sanderling for separate analyses. The main focus was upon Red-necked Stint (64.0% of observations) and Double-banded Plover (31.4%).

Double-banded Plover sheltered by tidewrack
  • Roosting birds were recorded on aged wrack 16 times more frequently than sand, and three times more than on fresh wrack.
  • Foraging birds were observed more than four times as often on aged wrack, when compared to fresh wrack or sand.
  • However, roosting on fresh wrack was more frequent in cooler, early-morning temperatures, for all waders and for the Double-banded Plover, when considered separately. Neither temperature nor absolute humidity were significant predictors of the proportion of Red-necked Stints roosting in areas with fresh wrack.
  • Foraging by waders (in general) and Double-banded Plover (in particular) was also more common within fresh deposits of wrack when temperatures were low and particularly if humidity was high. For Red-necked Stint, temperature alone predicted whether they were more likely to feed on fresh wrack, rather than aged wrack.

The importance of microhabitats

The authors show that sandy beaches with beach-cast wrack provide a complex mosaic of microclimates/habitats across differing substrates. Birds seem to exploit the microclimatic variation by using microhabitats that minimise energy expenditure, as both foraging and roosting were most likely to occur on the substrate providing the warmest, most energy-efficient conditions at the time.

There is well-documented evidence that food availability increases as seaweed decays, because wrack-beds provide homes for invertebrates, particularly developing larvae. This explains a predominance of foraging on aged wrack, which is likely to provide the best feeding opportunities. The key finding in this study is that tidewrack on sandy beaches provides important additional benefits for waders, by providing shelter and warmth. This may be particularly important when birds are fattening up for the next leg of a migratory journey. It is particularly interesting that, early in the morning, Double-banded Plovers and Red-necked Stints foraged within fresh wrack, the warmest available substrate at that time. Perhaps the effect of microclimate (temperature, humidity & shelter) might be usefully studied in other circumstances in which waders feed and roost?

The bigger picture

Turnstone, Sanderling, Purple Sandpipers and Dunlin on an Icelandic beach, having just crossed the Atlantic

When considering the role that coastal ecosystems play in the lives of waders, the main conservation focus has been on estuaries, as for instance discussed in Wader declines in the shrinking Yellow Sea. The open coastline is under threat too, squeezed by rising sea levels, battered by more frequent storms, polluted by plastic etc. In some areas, waders that use these habitats outside the breeding season are also prone to human (and canine) disturbance, as described in this Turnstone study.

Alongside more general habitat degradation, there are specific threats to tidewrack habitats along the coastline. This starts offshore, with the harvesting of stands of growing kelp, and continues when fresh tide-wrack is collected or cleared from shorelines. In 2018, it is estimated that 15,000,000 tonnes of brown algae were removed, globally. Traditionally, rotted tidewrack has been used as a fertiliser on nearby fields but most of the current output is collected when fresh and used to produce alginates, for food manufacture and biomedical purposes. Increasingly, attention is turning to use in biofuels, which has the potential to greatly increase the demand for seaweed.

Ringed Plovers in amongst seaweed on a Northumberland beach (UK)

Whilst the food, biomedical and energy industries see value in tidewrack, the tourist industry appears to see it as an untidy nuisance that spoils the image of a pristine beach. Who knows how much tidewrack is removed from beaches during daily grooming sessions or dug out of wader-rich corners before the start of the tourist season? If the image of what constitutes a welcoming beach is to be changed then perhaps there needs to be a focus on the interest that seaweed adds to a tideline walk – as visitors collect shells and look for amber, sea-coal and egg-cases. Is this naïve; have cotton buds, bottles and plastic sullied the image of tidewrack? Should we share more photographs of Sanderling chasing through seaweed-flecked spume and flocks of waders ‘chilling’ on banks of beautifully lit seaweed, instead of the barren white beaches that are used in holiday adverts?

As Timothy Davis and Gunnar Keppel conclude: “Beach-cast wrack created a complex mosaic of unique microclimates varying in space and time, which seemingly allowed shorebirds to minimize energy expenditure, by selecting the thermally most favourable habitats for roosting and foraging. Removal of beach-cast wrack therefore reduces habitat quality and increases energy expenditure and resources in shorebirds and may contribute to the observed decline of migratory shorebird species globally. Management of coastal ecosystems and shorebirds therefore needs to maintain fine-scale environmental heterogeneity.”

Paper

Fine-scale environmental heterogeneity is important for conservation management: beach-cast wrack creates important microhabitats for thermoregulation in shorebirds. Timothy John Davis & Gunnar Keppel. Journal of Applied Ecology. April 2021


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 wetlands, estuaries and non-estuarine coast are of international importance because of the numbers of waders that they support, with over a third of Europe’s wintering Oystercatcher, Ringed Plover, Bar-tailed Godwit, Black-tailed Godwit and Knot. (There’s more about these proportions in the WaderTales blogs: Ireland’s wintering waders and Do population estimates matter?).

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, but 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 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 2007/08 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 km 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 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 alongside, 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 below. 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 preference 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.

Grassland management for Stone-curlew

Detailed studies of a small number of Stone-curlews, breeding in Breckland in the east of England, give some clues as to how to provide the right habitat mix for these big-eyed, nocturnal waders. Increasing structural diversity, by ploughing and/or harrowing areas of grassland, can create an attractive network of nesting and foraging sites for breeding and non-breeding adults.

In a 2021 paper in Animal Conservation, Rob Hawkes and colleagues from the University of East Anglia, RSPB and Natural England give us insights into the daily lives of Stone-curlews nesting in the dry grasslands of East Anglia. By fitting five individuals with GPS tags and following their movements they were able to establish which habitats are used at different stages of the breeding season.

The Stone-curlew is the only migratory member of the thick-knee family. England is at the north-western limit of a breeding range that stretches east to the steppes of Kazakhstan, with birds wintering in southern Europe, North Africa, the Arabian Peninsula and the Indian sub-continent. Most English birds spend the winter months in Spain, Portugal, Morocco or Algeria but a small number are known to cross the Sahara. Stone-curlews return to East Anglia in March and April.

Unmodified grassland in the Brecks of East Anglia provides limited feeding opportunities for Stone-curlews
Creating heterogeneity within areas of grassland by ploughing and/or harrowing patches

During the twentieth century, numbers of Stone-curlew across Europe fell significantly, as mechanized farming expanded. The East Anglian population had dropped to fewer than 100 pairs by 1985 and it took huge conservation efforts to increase this to 200 pairs. Breeding birds are now typically to be found in sparsely-vegetated ground, often in spring-sown crops, on dry heathland or in semi-natural grassland areas, including those used for military training. Preferred food items, such as earthworms, soil-surface invertebrates, slugs and snails, are easier to find in areas of bare and broken ground than in thick grass, so grazing is an important part of conservation action on heaths and in grassland areas.

Each of these square treatments covers a hectare

The UK’s migratory Stone-curlew population has received a huge amount of conservation support, on the back of detailed studies of the species’ breeding ecology (Green et al. 2000).  Tremendous efforts have been made to maximise chick production in farmland, with conservation staff and volunteers working with farmers to monitor breeding pairs, so that they can protect nests and chicks during crop-management operations. In the long term, however, such interventions are too labour-intensive to be sustainable. Can equivalent benefits accrue if more Stone-curlews nest successfully in semi-natural grassland, where the costs of conservation subsidies are lower than in intensively farmed arable cropland?

The study that is reported in the 2021 paper in Animal Conservation took place in an extensive area of semi-natural grassland (nearly 40 km2) that is surrounded by a mosaic of arable farmland. The aim was to understand whether ploughing or harrowing patches of grassland can provide suitable foraging areas, and which other habitats are important.    

Tracking Stone-curlews

GPS tag attached to the back of a Stone Curlew

Stone-curlews are predominantly nocturnal feeders so some form of remote tracking device was needed to understand their movements. GPS loggers were fitted to five adult Stone-curlews during the breeding season. Individuals were caught at night using small, beetle-baited, elastic-powered clap-nets or in the daytime using nest-traps. Each individual was fitted with a 5.2 g solar-powered nanoFix Geo PathTrack GPS tag and an external whip antenna. GPS data were downloaded to a remote base station through a radio connection. Tagged birds were visited at least once a week to establish whether they were still nesting, if they had chicks or had finished breeding.

Where did they go?

One, two and three hectare plots of disturbed ground had already been created within Breckland’s grassland and heathland areas, prior to this study, as described in the paper and discussed in the blog Curlews and foxes in East Anglia. It was already clear that these plots were favoured as nesting sites but does disturbed ground also provide additional feeding opportunities for adult birds – including pairs nesting nearby on arable fields?

Using a telescope to point the base station ‘reader’ at a bird wearing a GPS logger

Three male and two female Stone-curlews were tracked for more than nine weeks (67 to 102 days), yielding 510 GPS fixes during nesting and 1371 post-breeding. There were some fixes in the pre-nesting phase and also during the chick-rearing phase but too few to be considered for analysis. Analytical methods are detailed in the paper.

During the nesting period, what was presumed to be the off-duty bird of each pair was found within 1 km of the nest on 90% of fixes. The mean distance from the nest during daytime feeding was about 100 m but, at night, tagged birds travelled five times as far, on average. They travelled furthest when heading for pig-fields and manure heaps.

  • Relative to closed, undisturbed grassland, nesting Stone-curlews were two- to three-times as likely to forage on disturbed-grassland during night and day, but especially during the day.
  • Night and day, ‘sugar beet or maize’ fields were used more than unmodified-grassland but similar to disturbed-grassland.
  • Nocturnally, Stone-curlews were ten-times as likely to use ‘pig fields or manure heaps’, when compared to undisturbed grassland.
  • The furthest distance travelled was just over 4 km, which is further than previously thought.
Stone-curlews will fly a long way to feed in pig fields

In the post-breeding period, tagged birds travelled up to 13 km to forage, with 90% of nocturnal foraging locations found to be within 5 km of day-time roosting sites.

  • Tagged birds were approximately 15-times as likely to use either disturbed-grassland or arable fallows when compared to undisturbed grassland.
  • Use of the category ‘pig fields or manure heaps’ was nearly as strong (factor c. 10), in comparison to undisturbed grassland.
  • Open crops in the categories ‘sugar beet or maize’ and ‘vegetable or root crops’ were also used more than undisturbed-grassland (factor c. 2).

Conservation messages

In England, there has been a long-term focus on trying to maximise Stone-curlew productivity within arable farmland, especially in East Anglia but also in Wessex. As suggested earlier, this is expensive – foregone production requires high subsidies and interventions by conservation staff are time-consuming. A French study, written up in Ibis by Gaget et al., seriously questions the viability of Stone-curlew populations within intensively managed arable farmland, even with conservation support. Given these problems, should conservation efforts focus on supporting and building up grassland populations?

In a previous tracking study, thirty years previously, Green at al. found that short semi-natural grassland provided suitable foraging habitat for Stone-curlews. Much has changed in Breckland in the intervening period, with the collapse of the rabbit population and an increase in the amount of outdoor pig-rearing. As the short swards of rabbit-grazed grassland have disappeared, Stone-curlews seem to have increasingly taken advantage of alternative opportunities offered in pig fields.

Previous attempts to replicate the grazing efforts of rabbits have involved increasing livestock numbers but this study shows that physical ground-disturbance interventions immediately and effectively create alternative foraging habitat. The authors suggest that multiple areas of disturbed-ground, close to the edge of large grassland blocks, can provide a network of nesting and foraging habitats, whilst allowing access to a mixture of feeding opportunities in the surrounding arable farmland. Of course, nobody is suggesting that intensive outdoor pig-rearing is a positive addition to the habitat mix, as it involves nutrient run-off, ammonia leakage into fragile plant-rich heathland, and pelleted feed attracts corvids (which are known to predate eggs).

The effect of creating ploughed or harrowed plots is almost immediate, in terms of prey availability. In more detailed studies of the effectiveness of slightly different ground-disturbance options, the research team found a strong selection preference only one year after the treatments were first implemented. In the longer term, these areas may become increasingly important, if young birds recruit to the local population and seek out these features. The researchers suggest that a bespoke, ground-disturbance agri-environment option might open up new breeding opportunities within semi-natural grasslands that are currently dominated by tall, closed swords. 

In England, conservation of dry grasslands and heathlands has tended to focus on the preservation on charismatic plant communities, an approach that may have been too gentle and conservative for other taxa. Whilst this study demonstrates that adding pockets of disturbed ground appears to benefit Stone-curlews, previous studies, conducted by this research team, showed benefits for Woodlark (Hawkes et al. 2019), Eurasian Curlew (Zielonka et al. 2019, summarised in Curlews and foxes in East Anglia), and rare, scarce or threatened dry-grassland invertebrates (Hawkes et al. 2019). Similar disturbance techniques have been shown to potentially benefit other grassland-breeding waders, such as Mountain Plovers (Augustine & Skagen 2014) and Upland Sandpipers (Sandercock et al. 2015) in North America, and Sociable Lapwings in Kazakhstan (Kamp et al. 2009).

Paper

This is a summary of a 2021 paper in Animal Conservation:

Effects of experimental land management on habitat use by Eurasian Stone-curlews. Robert W Hawkes, Jennifer Smart, Andy Brown, Rhys E Green, Helen Jones & Paul M Dolman.

Each summer, farmers, volunteers and conservation staff work together to monitor and protect nesting Stone-curlews on farmland, grasslands and heaths in eastern and southern England. Thanks to all of these people, the number of pairs of Stone-curlew in England is holding steady, at over 300 pairs. Progress was reviewed at a conference in 2017, as you can read in this layman’s report and this technical report. More guidance for landowners can be found here.


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.

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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.

Winter conditions for Whimbrel

Up until relatively recently, it was hard to study the same population of migratory waders in both its breeding area and its wintering grounds. Ringed birds established links between different countries but to follow a group of individuals through a complete annual cycle was nearly impossible. Geolocators, and more recently satellite tracking, are starting to enable scientists to piece together whole stories.

Camilo Carneiro and colleagues from the University of Aveiro in Portugal (Dep. Biology & CESAM) and the University of Iceland (South Iceland Research Centre) have been tracking Whimbrel travelling between Iceland and Africa for nearly ten years, using geolocators. In the latest paper to come out of this research they investigated carry-over effects; do conditions experienced in wintering locations affect breeding success?

How might carry-over effects work?

The conditions experienced during one stage of a migrant’s annual cycle may affect their performance in subsequent stages. Perhaps the resources available at a wintering site might affect the timing of spring departure and whether an individual has to stop off to refuel? In turn, such individual differences may be apparent in individuals’ arrival dates in the breeding area, and the condition they are in might affect laying date, clutch size, egg weight, etc?

Icelandic Whimbrel spend the wintering season anywhere between south-west Europe and the tropical coastal areas of West African countries such as Benin and Togo. Despite this huge non-breeding range, individuals are highly philopatric, travelling between the same breeding area and the same restricted wintering site on an annual basis, perhaps for twenty or more years. A Whimbrel flying to the Bijagós Archipelago of Guinea-Bissau covers nearly 6000 km, in the autumn, whereas a bird that only travels to the Tejo (Tagus) Estuary of Portugal flies not much more than half as far (see map). The ‘winter’ conditions they experience are completely different; short temperate days in Portugal or tropical heat in the mangroves in Guinea Bissau.

Camilo and colleagues were able to study Whimbrel in different wintering locations, in order to understand the conditions that are experienced by breeding birds from these areas. They measured annual return rates for birds that had flown different distances and experienced different conditions in the non-breeding season. Do Tejo birds, spending the non-breeding season in the coldest part of the wintering range, have a lower apparent chance of survival? Do those that make it through a Portuguese winter return to Iceland earlier and thereby increase their chance of breeding successfully?

Life on the wintering grounds

Camilo Carneiro has studied wintering Whimbrel in three sites – the Tejo Estuary (Portugal), the Banc d’Arguin (Mauritania) and the Bijagós Archipelago (Guinea-Bissau). Birds in the three sites experience very different conditions between the start of September and the end of March, as discussed in the paper and illustrated in the table below.

Hundreds of observations of individual Whimbrel and flocks provided information on feeding rates, diet and foraging time. Comparable food items were collected from the mud/sand substrates and the energetic values were calculated in the laboratory. Together, these data enabled a calculation of energetic intake. The Net Energetic Intake Rate varied markedly. The figure for the Bijagós is 3.9 times that of the Tejo and 1.4 times that of the Banc d’Arguin.

Crabs provide a large part of a Whimbrel’s winter diet

Birds have a basic running cost – the Basal Metabolic Rate – which is related to the size of the individual and ambient conditions it experiences. Those wintering in areas where they experience periods of colder and windier weather lose more heat and hence need more energy. The BMR was calculated as 2.17, 2.29 and 2.51 Watts for individuals wintering in the Bijagós, Banc d’Arguin and Tejo, respectively, showing that there are higher ‘running costs’ in northern sites. Whimbrels in the Bijagós never incurred energetic costs above BMR, whereas those in the Banc d’Arguin and Tejo had additional energetic costs on 20.6% and 9.7% of the winter days, respectively.

The daily energetic balance differed hugely. Whimbrels in the Bijagós experiencing an average energetic surplus of about 700 kJ/day, followed by 420 kJ/day in Banc d’Arguin and just 11 kJ/day in the Tejo. It should be noted that these figures are based only on day-time feeding.

A colour-ringed bird hiding in a Bijagós flock

Returning to Iceland

The research team has shown that Whimbrel can either fly directly to Iceland or stop off and refuel. It is thought that between 80% and 90% of journeys include a stop-over, typically in Ireland or western Britain. Direct flight takes four or five days. (see summary of previous papers and blogs below).

Whimbrels arrive back in Iceland between the end of April and late May, quickly taking up territories unless there is snow cover. Regular visits to the main study area in the Southern Lowlands helped to ascertain which colour-ringed birds had returned when. Nests are found, and eggs are measured and ‘floated’, to estimate the laying date.

During incubation, attempts were made to catch marked individuals that were carrying leg-mounted geolocators. Adults trapped on the nest are measured, unringed birds are marked and three to five feathers are removed from the breast. These feathers will have been grown in the bird’s wintering area and carry an isotopic signature from that region.

Using stable isotope analyses of the breast feathers, ground-truthed by birds tracked using geolocators, Camilo managed to assign the winter location to 180 Whimbrels. 159 had flown from the tropical region (which includes Bijagós), while 20 had spent the winter in the arid region (which includes Banc d’Arguin) and one in the temperate region (Tejo). When linking the wintering region to breeding phenology and investment, the research team found that:  

  • There were no differences in the size of the birds returning from the tropical and arid regions.
  • There was no difference between the probabilities of a bird successfully returning from the tropical and arid regions.
  • The timing of nesting and the volume of the eggs that were laid by females was not different for birds from the tropical and arid regions.

Where to spend winter?

Only one marked bird definitely wintered in temperate southwest Europe, which is not surprising given that there are not large flocks of Whimbrel in the estuaries of this area. This bird was excluded from the analyses but we know that it will have travelled much less far than birds wintering in Africa and experienced winter conditions in which it could barely meet its daily energy requirements.

Individuals wintering in the arid region, including birds in the Banc d’Arguin, travelled a lot further than birds wintering in southwest Europe. These birds had an expected surplus of 420 kJ per day on an average day but strong winds meant that there were 20% of winter days in which conditions were sub-optimal.

Trying to find Whimbrel in a sandstorm in Banc d’Arguin

Individuals wintering in the Tropical group, including birds in the Bijagós, travelled 900 km further than the Arid group but found more predictable weather conditions, achieving an estimated spare energy capacity of 700 kJ per day, without days with energetic costs above BMR. The authors point out that this energy surplus will likely be needed during long periods of moult and to fuel spring migration.

The authors conclude that any costs associated with having to fly further to reach the tropical region are compensated for by benign conditions. This does not mean that an individual bird makes a choice between Tejo, Banc d’Arguin and Bijagós. Happenstance may determine where a juvenile ends up in its first winter and philopatry means that, if alive, it continues to spend subsequent winters in the same area. Presumably the risks incurred by flying further (to Bijagós) balance out the risks incurred by wintering in a less predictable environment.

Life in and amongst the mangroves of the Bijagós

Very few Whimbrel spend the winter on the Tejo, in Portugal, and calculations in the paper suggest that there is a high risk of not being able to find enough food. This would probably translate into high mortality and explain low numbers.

Carry-over Effects

Although no carry-over effects were found, the authors discuss ways in which they may show up in other traits. There is an interesting discussion as to how carry-over effects might link experiences in the wintering grounds to breeding output in the next breeding season. Amongst other things, the authors suggest that differences among individuals using different wintering sites may only become evident if assessed over several years. We know that conditions are less benign in Banc d’Arguin, for instance. Perhaps there are years when conditions are bad enough for long enough to influence survival or body condition in spring. In such a year, there could be impacts on the ability to migrate, an increased likelihood of dying during migration or delayed breeding. It is possible that longer-term studies will pick up differences in return rates and/or breeding success for birds wintering in different areas? We shall see.

Paper

Linking range-wide energetic trade-offs to breeding performance in a long-distance migrant Camilo Carneiro, Tómas G. Gunnarsson, Verónica Méndez, Amadeu M.V.M. Soares & José A. Alves

Previous research on Icelandic Whimbrel

This Whimbrel, photographed in Bijagós is wearing colour-rings that were fitted in Iceland

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

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

Further reading

The following WaderTales blogs all consider how migratory behaviour might affect breeding season success, although without the direct measurements for individuals that have been carried out in the Whimbrel study.

Overtaking on migration shows that potential costs of migrating further can be overcome by undertaking early spring migration to staging sites that are closer to breeding areas.

Travel advice for Sanderling summarises research to understand the pros and cons of spending the non-breeding season in widely different locations.

Gap years for sandpipers is based upon a Peruvian Semipalmated Sandpiper paper that investigates the survival advantage of not migrating north to breed in a particular year.


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.

England’s Black-tailed Godwits

Back in 1976, all of the UK’s fifty pairs of Black-tailed Godwits were breeding in the Ouse Washes, which cut across the Norfolk/Cambridgeshire border in eastern England. Over the next thirty years, Ouse Washes numbers collapsed and the Nene Washes (near Peterborough) became home to forty or more pairs. What demographic processes were at play that led to this 24 km shift in the population centre and are there lessons to be learnt about the future conservation of England’s limosa Black-tailed Godwits?

43 years of breeding Black-tailed Godwits

The Washes of England represent a westerly extension of the breeding range of limosa Black-tailed Godwits, the focus of which is the Netherlands. This is a subspecies that’s in serious trouble; there has been a 75% decline in the Dutch population, as you can read here. The RSPB has invested in the conservation of Black-tailed Godwits for over forty years, most recently as part of Project Godwit, a partnership with WWT. In a 2021 paper in Wader Study, Mo Verhoeven and colleagues compare detailed studies in the period between 1999 and 2003 with more recent work (2015-2019) to try to understand how changes in demographic rates (productivity, survival and recruitment) have impacted upon the number of breeding pairs.

This study focuses on Black-tailed Godwits on the Low Wash, an area of the Nene Washes that is managed by RSPB. After periods of high rainfall, these areas are flooded to store excess water, mainly in the winter months. Fieldwork during the two periods of intense monitoring (1999-2003 & 2015-2019) included:

  • Searches for marked birds, when they return in March and April and throughout the breeding season.
  • Locating nests in April and then following breeding attempts (measuring and weighing eggs, to back-calculate to lay-dates, and monitoring nesting success).
  • Ringing and colour-marking chicks.
  • Nest data loggers and cameras were used in the later period (2015-2019), to help establish timing of predation events.
  • Adults were trapped on the nest (2015-2019), to add rings, colour-marks and, in some cases, geolocators.

The switch to The Nene  

Back in 1975, all of the limosa Black-tailed Godwits nesting in the UK were to be found in the Ouse Washes. The graph below shows the number of pairs nesting in the Ouse and Nene Washes, together with other regions of England. The two study periods (1999-2003 & 2015-2019) are highlighted. In 1999, at the start of the first period of intensive study, over half of pairs were in the Nene Washes, with a rapid increase in this proportion by 2003. The situation remained relatively stable through to the start of the second period of intensive study in 2015.

The graph showing the number of breeding pairs only runs through until 2017, as the number of breeding pairs in 2018 and more recent years has been affected by head-starting, the process of hatching chicks in incubators and raising them in captivity, through to fledging. The WaderTales blog Special Black-tailed Godwits describes the excitement and anticipation as the first 25 captive-reared chicks were released at the Ouse Washes. The first head-started birds returned in 2018.

Black-tailed Godwit chick being raised in captivity

In 1992, following multiple years of spring flooding at the Ouse Washes, the godwit population in the UK declined to only 19 pairs. There was a steady increase of godwits at the nearby Nene Washes and the UK population recovered to 53 pairs by 2006. Since then, the breeding population at the Nene Washes had been slowly declining until head-starting provided a welcome boost. See Head-starting Success and reports on the Project Godwit website.

Comparing the two periods

The early period of intensive work in the Nene Washes (1999-2003) took place when the population was increasing strongly, a trend that continued until 2006. The later period (2015-2019) coincided with a shallow decline. For conservationists, keen to maintain a UK population of breeding Black-tailed Godwits, it is important to understand the causes of the differences in population trends, if the right conservation solutions are to be deployed to resolve ongoing problems for this red-listed wader.

Adult survival: Large waders, such as Black-tailed Godwits, are long-lived birds (see Measuring Shorebird Survival) and it is unsurprising that the annual survival rate of Black-tailed Godwits nesting in the Nene Washes was found to be high, with an estimate of 88%. The short period of time available between ringing and potential observations for birds that were marked in the second period (2015-2019) meant that there were fewer sightings from which to calculate survival rates of birds from this recent period. Despite this smaller sample, the research team are confident that adult survival has not declined over time and is therefore not the cause of the change in population trend between the two periods.

This chick weighs 30.6 grammes (just over an ounce)

Nest Survival: The number of nests lost to flooding was very low indeed; none in the earlier period and only 1% in the later. Nest desertion rates were higher in the more recent period (7%) than during 1999-2003 (2%) but the differences are not statistically significant. The big change is in predation rates. Only 22% of the nests that failed in the period 1999-2003 failed due to predation but this more than doubled in 2015-2019. Analyses that took account of lay-date showed that the chance of hatching was much lower in 2015-2019 than in 1999-2003, irrespective of the timing of nesting attempts.

Chick survival: Given the increased predation of nests, it is perhaps unsurprising that the chick survival rates were also lower in 2015-2019 than in 1999-2003. Modelling suggests that a Black-tailed Godwit chick that hatched in one of the summers between 1999 and 2003 was between 2.4 and 3.6 times as likely to survive the first fourteen days of life as a chick that hatched between 2015 and 2019.

Explaining the patterns

The Ouse and Nene Washes are only 24 km apart but adults are highly site-faithful, and it is therefore likely that birds will try to nest in the same place in consecutive years, if at all possible. The Ouse Washes population was not marked at the time of the flooding events in the springs of the 1990s, so we do not know whether the growth in numbers on the Nene during this period was linked to flood-related declines on the Ouse. However, we do know that, when water levels are too high at either the Ouse or the Nene Washes, pairs will nest on nearby arable fields, just outside the flood plain. Nests on arable fields at the Nene have never resulted in successful fledging, so any such attempts near the Ouse in the 1990s may well have gone unnoticed.

As discussed in Site fidelity in Black-tailed Godwits, chicks are also highly philopatric (tending to return to the site from which they fledged). Of the 63 chicks raised on the Nene Washes, for which subsequent breeding locations have been ascertained, 61 have been found breeding in their natal area. This is the same pattern as found in the Dutch breeding areas. It is likely that the growth in numbers in the Nene Washes in the period 1977 to 2006 was driven by high productivity and subsequent local recruitment. The key question is therefore ‘why has breeding success declined since this time?’

Ringing a Black-tailed Godwit chick

Some causes of reduced breeding success can be ruled out. None of the 213 nests was trampled by grazing cattle (see Big Foot and the Redshank nest) and only one nest was flooded. This leaves predation as the main cause of low success. The authors suggest three things that might have changed:

Lower numbers of other waders: Over half of the other waders nesting in the Nene Washes study area disappeared between 2000 and 2016, with losses of 73% of breeding Lapwing, 46% of Redshank and 49% of Snipe. The number of Black-tailed Godwit nests increased during this period. These four species all work together to raise the alarm if a predator is present and to mob mammalian predators such as fox and stoat. Reduced overall wader numbers could have reduced predator deterrence and will certainly have meant that there were fewer nests of other waders for predators to find.

Predated Black-tailed Godwit nest

Reduction in non-wader prey: The number of Pheasants in the area surrounding the Nene Washes is thought to have decreased, with reductions in the numbers released for shooting. Fewer pheasants around during the breeding season may result in a reduction in the availability of Pheasant eggs, sitting females and chicks. The lack of this food could have increased predator pressure on breeding waders.

Broader suite of predators: Badgers, Common Buzzards and Red Kites have colonised the area and Marsh Harrier numbers have increased. Badgers are known to target ground-nesting birds and avian predators take eggs, chicks and occasional adults.

What to do next?

Head-started chicks in the Project Godwit release cage

The head-starting project has been designed to give a short-term boost to numbers of breeding Black-tailed Godwits on the Ouse and Nene Washes. In the longer term, Project Godwit aims to improve habitat management in ways that can lead to increased productivity, without head-starting. The authors identify several actions to try to increase productivity, which include:

  • Maintain the openness of the wader nesting area, by removing trees, reed beds and rushes, in which predators can perch, nest and hide (there’s more about this in Mastering Lapwing conservation).
  • Attempt to increase the abundance of alternative prey (small mammals) in the surrounding landscape (see Can habitat management rescue Lapwing populations?).
  • Provide diversionary food for key avian predators (see Deterring birds of prey).
  • Use a mixture of fences and predator control (see Toolkit for wader conservation).
  • Flood the grassland in the winter period, to reduce numbers of small mustelids (stoats and weasels) in the godwit nesting areas and concentrate small mammal prey (e.g. mice and voles) on the edges of the Nene Washes.

Some additional thoughts (not in the paper)

The growth in the Nene Washes population of Black-tailed Godwit between 1977 and 2006 suggests that Black-tailed Godwits can do well in the right circumstances. Perhaps there are other areas of lowland wet grassland – especially ones with low predator densities or effective predator management – in which head-started individuals might thrive?

Having a muddy time in Portugal

An annual survival rate of 88% means that only about one in eight adults dies in a given year. If survival rates change then that can have a major effect on the viability of a small population. The reliance of limosa Black-tailed Godwits upon a limited number of habitats and key sites in the non-breeding season, especially in Portugal, Spain and Senegal, make them very vulnerable to changes, whether brought about by climate, new farming systems (especially rice growing) or habitat removal (see blog about planned airport in Tagus estuary. The conservation of limosa Black-tailed Godwits is a flyway-scale challenge, as outlined in this action plan, produced by AEWA.

Read more

Diagnosing the recent population decline of Black-tailed Godwits in the United Kingdom. Mo A. Verhoeven, Jennifer Smart, Charlie Kitchin, Sabine Schmit, Mark Whiffin, Malcolm Burgess  and Norman Ratcliffe. Wader Study.

This study was jointly funded by the RSPB and Natural England through the Action for Birds in England Partnership and through an EU LIFE Nature Programme project (LIFE15 NAT/UK/00753 – LIFE Blackwit UK) in partnership with the Wildfowl & Wetlands Trust with support from the National Lottery Heritage Fund via the Back from the Brink Programme.


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.

Following Sociable Lapwings

Understanding the migration routes of threatened migratory species is key to supporting declining populations.

Targeted help for the critically endangered Sociable Lapwing has come another step closer, thanks to the publication of a paper by Paul Donald and colleagues in the Journal of Ornithology.  In it, they describe how satellite tracking, colour-ringing, studies of historical records and flock counts have combined to give a much clearer picture of the main sites used by Sociable Lapwings during migration and in the winter. In addition, the research team’s work has produced a more robust estimate of the world population of the species. Given the threats that Sociable Lapwings face when they are away from their breeding sites – particularly from hunting – this is all crucial information for their conservation.

The Sociable Lapwing

Nesting close to a village

Sociable Lapwings once bred from Ukraine through to western China. There still may be a small population in southern Russia but the breeding range is now almost entirely restricted to the steppes of central and northern Kazakhstan (Sheldon et al 2012). For centuries, Sociable Lapwings have relied upon grazing by herds of Saiga Antelopes, which created open areas in which to nest. As natural grazing systems have broken down, Sociable Lapwings have become increasingly restricted to grazed land around villages (Kamp et al. 2009). Given that current productivity levels appear sufficient to maintain this small population in a viable state, low adult survival is thought to be the most likely driver of recent population declines (Sheldon et al. 2013).

Prior to this study, little was known about the wintering areas used by Sociable Lapwings. There had been some reports of flocks in eastern Africa but most information from countries such as Sudan was several decades out of date. Further east, sightings in Pakistan and India accounted for only small numbers of the known population. Did birds travel straight from breeding areas to winter sites or were there key stop-over sites that were missing from the map? Did birds in the western part of the breeding range head southwest to East Africa, with those in the east heading south to Pakistan and India? It was time to track some birds!

Distribution map from BirdLife International data zone

Detective work

Colour-ringed individual

Paul Donald and colleagues undertook a long-term study of the movements of Sociable Lapwings, using satellite tagging, colour-ringing, targeted field surveys and a database of historical and recent sightings. The collation of this database involved a huge amount of painstaking work, with researchers checking museum collections, searching through unpublished literature, liaising with local birdwatching organisations and looking for bird lists and images, via the Internet.

Studies of breeding birds were mainly focused upon an area around Korgalzhyn, in central Kazakhstan where, between 2004 and 2015, 150 adult Sociable Lapwings and 1473 chicks were colour-ringed. The main aim was to estimate survival rates but some of these marked individuals provided valuable data when seen during visits to potential wintering and passage sites. Most of this fieldwork outside of the breeding season was undertaken by local conservationists and ornithologists, with their efforts being coordinated by the BirdLife International Social Lapwing Project.

Releasing a satellite-tagged bird

Detailed information on movement patterns was collected with the assistance of 29 satellite-tracked adult birds, caught in the breeding grounds between 2007 and 2015. Most were tagged near Korgalzhyn, in central Kazakhstan but five were tagged in an area about 800 km further east. Of these 29 birds, 21 were female. Technical developments by Microwave Telemetry Inc. meant that early 9 g solar-powered tags could be replaced by 5 g tags in later years.

Tracked birds

The paper by Donald et al contains detailed information about the movements of individual birds and how they were tracked. Anyone contemplating a similar study may want to read about how data were filtered and ‘clusters’ and ‘transit points’ were defined.

Early (larger) tags did not produce as much information as later (smaller) tags. The fact that one of the early-tagged birds was seen back on the breeding grounds without its harness and tag suggests that harness failures may have been an issue early on. 16 of the 29 tags provided data that enabled the research team to plot 27 complete autumn migration journeys and 13 complete spring journeys. Some birds were tracked for longer periods, producing data for two or more autumn (7 birds) and spring (3 birds) migrations. Birds followed for more than one year repeated almost exactly the same autumn and spring journeys.

Note the short vegetation

The tracked birds set off on one of two routes at the end of the breeding season, either heading west and south to northeast Africa and the Arabian Peninsula (the western route) or due south to Pakistan and India (the eastern route):

  • Seventeen birds used the longer western route, west across Kazakhstan, across or around the western Caspian Sea, then south through the Caucasus and the Levant, before reaching wintering areas in Saudi Arabia and eastern Sudan (map below).
  • Seven birds set off on the shorter eastern route, due south to Turkmenistan and Uzbekistan, then over or around the mountains of northern Afghanistan to wintering areas in Pakistan and north-western India.
  • Migration direction was ascertained for 22 birds from the central Kazakhstan group: 16 birds took the westerly route and 6 used the eastern route. Only two of the birds that were marked further east produced usable tracks, with one bird following the eastern route and one following the western route.
  • Birds using the eastern route travelled an average of 2839 km, with birds on the western route travelling 5199 km – nearly twice as far. Birds on both flyways departed their breeding grounds and arrived on their wintering ground at around the same time. Key stop-over areas were identified (see paper).
This tagged bird was photographed in a flock in Pakistan
  • In autumn, birds on the eastern route stopped only once, at Tallymarzhan (on the border of Turkmenistan and Uzbekistan), remaining in the area for between 29 and 48 days. Western birds stopped more often and generally for much shorter periods.
  • Central Azerbaijan and northern Afghanistan seem to be important spring staging sites for birds on the western and eastern routes, respectively, but these sites have yet to be surveyed.
  • The timing, direction and use of stopover areas of birds tracked in more than one year were highly consistent but there was much variation between individuals.

Only eight of the Sociable Lapwings colour-ringed as chicks on the breeding grounds in central Kazakhstan were subsequently seen outside Kazakhstan: five at the Kuma-Manych Depression in Stavropol (on the western route) and three at Tallymarzhan in Uzbekistan (eastern).

Three recently-fledged youngsters

Chicks and adults gather in mixed flocks prior to migration and it is thought that they migrate together. Perhaps circumstances and the adult birds with which young birds happen to associate determine the direction of the first migration south. If it is still alive, why should a young bird migrate in a different direction in a subsequent year?

Adults used up to three different areas during the course of a winter and, as far as could be determined from the small number of multi-year tracks, did the same thing in subsequent years. An analysis of the sites used by wintering birds emphasised the importance of arable habitats – most stopover sites are in areas that have been under cultivation for over 2000 years.

There was little evidence of strong breeding site fidelity, with adult birds moving up to 300 km from the site of tagging in the next year. For a species that may need to search for nesting sites in recently-grazed or burnt-off grassland, within a relatively homogeneous steppe habitat, it is perhaps unsurprising that there appears to be less of a tendency for birds to be site-faithful than seen in many other species of wader.

Finding the flocks

The research team found that their database of historical and recent records of flocks of migrating and wintering Sociable Lapwing identified the same two major migration routes that appeared from traces of tracked birds. There is a strong suggestion that there is a third, central route that takes birds to Oman, parts of eastern Saudi Arabia and to sites around the Persian Gulf and the Gulf of Oman. None of the 29 tagged birds happened to end up in these areas.

Counts on both sides of the border between Uzbekistan-Turkmenistan, in the autumn of 2015, suggested that between 6000 and 8000 Sociable Lapwings may use this area when migrating along the eastern route. Using information on the proportion of tagged birds that visited this area, and for how long, the research team estimate that the global population of Sociable Lapwings is about 24,000 individuals, although the 95% confidence interval is broad (13,700 to 55,560 birds).  The estimate is the most robust so far and the methodology can be repeated in the future, in order to monitor population change.

The bigger picture

In Palaearctic species with intercontinental flyways to both Africa and Asia, individuals breeding in the western part of the range usually take the western flyway and those in the eastern part of the breeding range migrate along an eastern flyway, with a clear migratory divide within the breeding range. This is the case for species as diverse as waders, bustards and bee-eaters. Discovering that Sociable Lapwings are not so similarly constrained was a surprise, with the route used being independent of the longitude of the tagging site.

Post-breeding moulting flock in central Kazakhstan

During migration and on the wintering grounds, Sociable Lapwings are strongly associated with areas of agriculture, particularly along rivers. Only in northern Syria and and Tallymarzhan were birds found in more natural steppe grasslands. Birds are now using irrigated areas of the Arabian Peninsula, where agricultural land has been created in former deserts. It appears that new generations of Sociable Lapwings, taking advantage of these novel opportunities, now undertake shorter migratory journeys and have perhaps established new pathways. This form of Generational Change is the subject of a WaderTales blog about Black-tailed Godwits.

Sociable Lapwings are widely dispersed over huge and often inaccessible areas on both the breeding and wintering grounds. Their concentration in a small number of predictable staging areas, during migration, offers the best opportunity to gather information on population trends. Birds using the western route appear to have more available options than birds in the east, making numbers harder to monitor.

Birds using the western route, particularly in Syria and Iraq, are targeted by hunters in the autumn and there is no protection for any of the stopover sites identified in this study. The authors suggest that it is particularly important to know more about spring staging areas in Azerbaijan, as this is a focal area for returning birds using the western route and potentially an area in which hunting takes a significant toll. Birds using the eastern route appear not to be hunted – or at least not in the same sort of numbers as in the west. Sociable Lapwings that use the less well-understood central route and that winter in the Arabian Peninsula may be vulnerable, as they share irrigated fields with species that are popular with hunters.

To learn more

The authors, and everyone else who has contributed to decades of Sociable Lapwing research, are to be commended for the work they have done. Now that key sites have been identified, it is to be hoped that there is political will to provide protection for this critically endangered species. Actions will need to include site designation, local involvement in conservation action and concerted efforts to curb illegal hunting.

Part of a flock of pre-migratory birds in central Kazakhstan (409 birds were counted)

The paper upon which this blog is based is:

Migration strategy, site fidelity and population size of the globally threatened Sociable Lapwing Paul F. Donald, Johannes Kamp,Rhys E. Green, Ruslan Urazaliyev, Maxim Koshkin & Robert D. Sheldon. Journal of Ornithology.

Other WaderTales blogs about tracking projects that help to identify migratory hot-spots used by threatened waders include:

Spoon-billed Sandpipers: Track and Trace (finding wintering and passage sites)

Black-tailed Godwits are on their way home (Tagus Estuary airport plan)

Teenage Waders (Hudsonian Godwits in the Pampa wetlands of Argentina)


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.

WaderTales blogs in 2020

Around the world in sixteen blogs

2020 was a strange year, as covid swept around the world and more and more of us faced travel bans. Throughout it all, waders/shorebirds continued to fly thousands of kilometres in spring and autumn.

Five out of sixteen of the year’s WaderTales blogs focused on international migration studies, using a mixture of colour-rings, geolocators and satellite tags. It was particularly interesting to think more about ‘teenage’ waders – the period between fledging and first breeding. It may be a couple of years or more before shorebirds return to their breeding grounds; what do we know about what happens during this period? Are vulnerable and threatened species and the sites that they rely on receiving enough conservation support during these important, teenage years?

  • Teenage waders is ostensibly about Hudsonian Godwits that spend the non-breeding season in Chile and breed in Alaska. Juan Navedo & Jorge Ruiz noticed that a small number of satellite-tagged birds headed for Argentina instead of Alaska in April. This led to the discovery of flocks of young Hudsonian Godwits (and adults that choose not to breed in a particular year) in the pampa wetlands – areas that are under threat from industrial-scale farming.
  • Spoon-billed Sandpipers: track & trace follows tagged Spoon-billed Sandpipers, as they travel from their breeding sites in Russia, through China and beyond. This is an amazing story; thirteen birds carrying back-mounted transmitters have revealed information that will enable the targeting of conservation measures to support a global population that is estimated to be just 660 birds.
  • Gap year for sandpipers is based upon a Peruvian Semipalmated Sandpiper paper that investigates the survival advantage of not migrating north to breed in any particular year. It reveals that taking a gap year may be a sensible strategy in some circumstances.
  • Which Icelandic Oystercatchers cross the Atlantic? Around 30% of Oystercatchers remain in Iceland for the winter, with the rest of the population flying south across the Atlantic in autumn. Having made an initial ‘decision’ to be a resident or a migrant, an individual sticks to this strategy but what determines whether a particular Oystercatcher becomes a migrant?
  • A Rhapsody of Whimbrel asks whether Whimbrel use time and weather cues in their travel ‘planning’ and whether their plans change during the course of their lives. By looking at weather patterns encountered by tagged birds, flying between western Africa and Iceland, Camilo Carneiro shows that old birds may be able to learn new tricks.

A Scottish trio

2020 seems to be the year of the Scottish WaderTales blog, with three spring/summer stories about research led by RSPB Scotland staff.

  • Migration of Scottish Greenshank summarises a study of a small number of breeding birds, using a mixture of colour-ring sightings and geolocator records. Unlike their cousins, that breed in eastern Russia and migrate to Australia or even New Zealand, Greenshank nesting in northern Scotland are short -distance migrants, mostly staying within Britain & Ireland for the whole of their lives
  • Trees, predators and breeding waders is all about how the presence of woodland affects the distribution of mammalian predators, even after the trees have gone. Species such as Curlew and Dunlin are benefiting from the removal of forestry plantations from the peat blogs of Forsinard, in north-east Scotland. We discover that it takes a long time for habitat restoration to deliver conservation benefits because of residual levels of predator pressure.
  • Scotland’s Dotterel: still hanging on discusses how climate changes are affecting the distribution and numbers of Scottish Dotterel. High up on the Cairngorm plateau, scientists have been studying the links between Dotterel numbers and climate change. The distribution of nests seems to reflect local weather conditions but declining numbers may be more of an African problem.

Nesting waders

  • Where to nest? Almost all waders/shorebirds nest on the ground which means that nests are vulnerable to predation. Two main strategies have evolved to minimise egg losses, cryptic egg colouration in open settings and hiding nests in vegetation. A study in Iceland investigates which strategy appears to be more successful and in what circumstances. Do Iceland’s open-nesters (Oystercatcher, Golden Plover & Whimbrel) fare as well as nest-hiders (Redshank, Snipe & Black-tailed Godwit)?
  • Curlews and foxes in East Anglia raises some interesting conservation issues. Might it be possible to attract breeding Curlew to patches that can be protected from potential predators? Habitat improvement measures that have been designed to help Stone Curlews are popular with Curlews too. Could shallow soil disturbance be used to support Curlew conservation?

Black-tailed Godwits

WaderTales started out as a way to provide feedback to the volunteers who report colour-ringed Black-tailed Godwits. Most of the twenty blogs about the species refer to islandica but the two in 2020 focus on limosa. The first blog is a follow-up to the 2019 story about a plan to build a new airport within the Tagus Estuary. This threatens to undo much of the good work of Project Godwit – trying to rebuild the English breeding population in the Fens. To raise money for this project, Jen and Mark Smart cycled 1000 km across England, vising many of the sites where head-started Project Godwit chicks have been seen. It was a great opportunity to provide updates on the migration stories of these special birds.

  • Black-tailed Godwits are on their way home reveals the importance of the Tagus Estuary (Portugal) to England’s breeding limosa Black-tailed Godwits.
  • Cycling for waders is about the head-starting initiative to rebuild the English breeding population of Black-tailed Godwit – and a sponsored cycle ride to support Project Godwit & International Wader Study Group.

Behaviour

Two of this year’s blogs are about bird behaviour, other than migration.

  • Disturbed Turnstones focuses upon a paper about the changing distribution of Turnstone in northeast England. As numbers have declined, birds have withdrawn from beaches with more people and dogs. Off-shore roosts seem to have become increasingly important.
  • Flagging up potential problems discusses safety issues associated with using flags and flag-mounted geolocators when studying waders. At the heart of the blog is a study of Common Sandpiper survival and migration but there is additional information about ways to minimise problems that may occur when using leg-flags.

Book reviews

Occasionally, the publication of a new book about waders/shorebirds is used as a hook upon which to hang a WaderTales blog. Two new books, Red Sixty Seven and Flight Lines, were treated in this way in 2020.

  • Nine red-listed UK waders discusses why nine species of wader find themselves on the UK red list of species of conservation concern). The book, which covers all of the 67 species on the UK Red List, is raising money to help fund scientific research by BTO and RSPB.
  • Plovers from the north is a blog about the global migration patterns of Grey Plovers (Black-bellied Plovers). There is an Australian focus but this was a good opportunity to summarise recent research from around the world.

Previous summaries

WaderTales blogs in 2019

WaderTales blogs in 2018

WaderTales blogs in 2017

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

Gap years for sandpipers

Will this Semipalmated Sandpiper fly north to breed?

With the approach of spring in the Northern Hemisphere, waders (shorebirds) that have spent the previous few months on the shores of Africa, the Americas, Asia, Australasia, Europe and oceanic islands need to decide whether to fly north. Those that depart leave behind flocks of young birds, together with adults that ‘choose’ not to migrate north and attempt to breed. In a paper in Movement Ecology, Eveling Tavera and colleagues investigate how the decisions made by individual Semipalmated Sandpipers that spend the non-breeding season in Paracas (Peru) are likely to affect their chances of survival.

Semipalmated Sandpipers

The Semipalmated Sandpiper is one of the smallest of the world’s waders. The species is designated as near-threatened by BirdLife International and IUCN, despite its large breeding range. In their assessment, they draw attention to declining numbers, potentially linked to reduced food supplies in staging areas and to changes to arctic breeding habitat. Hunting pressure in some parts of the wintering range (especially the eastern seaboard of South America and in the Caribbean) may particularly affect Semipalmated Sandpipers that breed in eastern Canada.

Back in the 1970s, when I spent three summers in James Bay (northern Canada), I remember catching skinny juvenile Semipalmated Sandpipers that weighed under 20 g, which is way smaller than a House Sparrow (24.2 g – 30.7 g: BTO BirdFacts). We also caught fat, 40 g  adults that were about to leave and head to countries such as Suriname in South America, perhaps stopping off in the Bay of Fundy on their way south. In just a few months, it would be time to fly north again and I guess we assumed that any bird that was alive would at least try to make the return journey. After all, these are small shorebirds and most small shorebirds breed in their first year.

The distribution of Semipalmated Sandpipers during the non-breeding season covers a broad range of latitudes, from about 25°N (southern Florida) to 23°S (northern Chile and southern Brazil). Some of the birds flying to Arctic Canada, Alaska and Northeast Russia are travelling a lot further than others. A bird setting out on a return journey to northern Quebec from Peru will need to find more resources to fuel its journey than one flying from the Caribbean. The additional fattening requirement could potentially affect the ability of individuals to make the return migration.

Shorebird Survival

Graph from Méndez et al in Ibis

In their global review of annual survival rates of shorebirds, Verónica Méndez and colleagues were able to include 56 species from around the globe. Unsurprisingly, small waders tend not to live as long as larger species. Combining the various studies of Semipalmated Sandpiper, they estimated an annual survival rate for adults of 0.61 (see Measuring shorebird survival). This means that, on average, there’s a 39% chance of an individual dying between one breeding season and the next.

We know that waders don’t always breed every year, as discussed in Teenage Waders. Small waders have lower life expectancy than large waders (Waders are long-lived birds) so missing out on a breeding season makes much more of a difference to a small sandpiper than to a Knot (estimated survival rate 0.8 or 20% chance of dying within the next twelve months) or an Oystercatcher (0.89; 11%).

As Tavera et al point out in the introduction to their paper, although most small shorebirds attempt to breed in their first year of life they may have lower breeding success than older individuals. In Semipalmated Sandpipers, young birds start nesting later in the spring, lay smaller and fewer eggs, and produce fewer chicks (references in paper). When comparing potential reproductive output, a bird that does not migrate north in its first year is probably missing out less than an adult that ‘takes a year off’.

Breeding habitat in Alaska – a long way from Peru

Semipalmated Sandpipers in Peru

The results presented in the Tavera et al Movement Ecology paper come from a long-term Semipalmated Sandpiper colour-ringing study in the Paracas National Reserve, 250 km south of Lima, in Peru. Over a period of five years, 1963 birds were caught in mist nets and individually marked, producing 3229 resightings. Only eight of the marked birds has been seen during the nesting season, all in Alaska and western Canada. This paper builds on a previous paper: Effects of migration distance on life history strategies of Western and Semipalmated sandpipers in Perú.

The key findings in the study are:

  • 28% of first-year Semipalmated Sandpipers remain at Paracas, instead of heading north
  • 19% of adults remain in Paracas instead of migrating.
  • The apparent annual survival rate of first-years that head north is 0.555, compared to 0.671 for first-years that stay at Paracas.
  • For adults, apparent annual survival rate of those that migrate is 0.614, compared to 0.808 for those that stay.

The fact that 28% of youngsters in this particular population of Semipalmated Sandpipers don’t migrate north in the first year was unexpected, given what had been learnt from previous studies of the species, but the fact that one in five adults ‘choose’ not to breed in any year is probably more surprising. In a species with a declining population, these missed opportunities to boost the population appear concerning.

Short and long bills

Measuring bill length

Several thousand Semipalmated Sandpipers spend the non-breeding period at Paracas, including individuals with long bills (which are thought to fly there from eastern Arctic breeding populations, about 8,000 km away) and short bills (likely from western Arctic breeding populations, up to 11,000 km distant). There is more about these morphometric differences in this paper by Cheri Gratto-Trevor et al in Waterbirds.

It is not possible to assign individual Semipalmated Sandpipers to a particular population, especially as there are also sex-based differences in bill length, and gender could not be determined in the hand. However, there is a trend for longer-billed birds to be from the east. The eight colour-marked birds from Paracas that have been seen in the western part of the breeding range were all short-billed or intermediate-billed birds.

  • Larger-billed juveniles appear more likely to migrate than smaller-billed juveniles, suggesting that Semipalmated Sandpipers that have travelled less far are more likely to breed in the first year.
  • Resightings of flagged birds suggest that the survival of first-year birds that fly to the Arctic in their first spring is markedly lower in small-billed birds than in long-billed birds.

The cost of migration seems particularly high in small-billed, first-year Semipalmated Sandpipers. These birds tend to be longer-distance migrants, from the western end of the breeding range.

Modelling the costs and advantages of migration

Eveling Tavera and her colleagues have found that survival is higher for Semipalmated Sandpipers that stay in Paracas than for migrants. During the period April to September, the apparent survival rate for first-year birds and adult birds is much higher for birds that do not migrate.  The survival advantage acquired by non-migrants is significantly greater for adults (0.215) than for yearlings (0.140).

Clutch of Semipalmated Sandpiper eggs

By failing to migrate, individual Semipalmated Sandpipers miss out on a breeding opportunity. Does a bird that lives longer but does not breed in every potential year produce more youngsters than a bird that lives a little less long but breeds every year? In an appendix to the paper, the research team calculate whether the survival advantage for birds that stay in Paracas is high enough, in fitness terms, to compensate for the loss of potential youngsters. They used values for annual survival, mean clutch size and hatching success from studies by Weisser et al and Gratto et al, for adults and first-year birds, to produce figures for Lifetime Reproductive Success (LRS). The predicted survival advantage of non-migrating adults (0.240) is higher than that of first-years (0.134) because they forego a larger average potential reproductive output than do inexperienced birds.

Using these calculations:

Teamwork: birds are mist-netted at night
  • On average, a first-year migrant will have the same LRS as a bird that does not migrate if its survival in the first year is no more than 0.134 lower. This is close to the measured value of 0.140 for the Paracas birds.
  • On average, an adult migrant will have the same LRS as a bird that does not migrate if its survival in that year of life is no more than 0.240 lower. This is close to the measured value of 0.215 for the Paracas birds.

Based on the modelling of LRS and survival rates, the team conclude that ‘juvenile and adult birds staying at Paracas compensate for the loss of a breeding opportunity with higher survivorship than migrant birds’.

Different non-breeding populations

Tiny bill of an Alaskan Semipalmated Sandpiper

The Semipalmated Sandpipers that breed across North America and the far eastern tip of Russia travel to a wide range of destinations in the autumn, with birds mixing in the non-breeding season. The Paracas site is a long way from the species’ breeding grounds and the results may suggest that migration is constrained by distance. However, there could be other processes at play, especially if food supplies are limited at the time when individuals need to fatten up for migration. Jeroen Reneerkens et al showed that Greenlandic Sanderling that spend the winter near the equator (Mauritania & Ghana) had lower apparent survival rates than birds that travelled much further south (Pretoria). They were also less likely to breed in their first year than birds spending the breeding season in other locations, and arrived on their breeding territories late in the season. Migration distance is not always a problem, it transpires, as long as there are refuelling possibilities on the way north, as described in Travel advice for Sanderling. This is also discussed in Overtaking on Migration, a Black-tailed Godwit blog based upon a paper by Alves et al.

Conservation importance

Much of the statutory protection for migrant waders is based upon sites used in the non-breeding season. Eveling Tavera has shown that Paracas is important for the whole year. Are there other sites that hold 20% or more of their flocks of Semipalmated Sandpipers for the whole year? What are the conservation implications for this species, which is already designated as ‘near-threatened’? Are we doing enough to look after pre-breeding (and non-breeding) flocks? This issue is discussed further in Teenage Waders, built around a Hudsonian Godwit paper by Juan Navedo & Jorge Ruiz.

In conclusion

An individual Semipalmated Sandpiper does not, of course, have the experience or capacity to enable calculation of differential survival rates. The decision to migrate north will be based upon circumstances and the bird’s condition. Effectively, it is trading off the fitness benefit of higher survival against the fitness cost of a foregone breeding opportunity – but it does not know that that is what it is doing. What is interesting, in this study, is that the cost-benefit analysis so closely matches what is found using field data from this particular site. The survival rates and percentage of non-breeding Semipalmated Sandpipers in Suriname or at another site in Peru may well be completely different but could still balance out. There is so much more to learn about shorebird migration.

Oversummering juvenile and adult Semipalmated sandpipers in Perú gain enough survival to compensate for foregone breeding opportunity Eveling A. Tavera, Glenn E. Stauffer , David B. Lank and Ronald C. Ydenberg. Movement Ecology 8,42. https://doi.org/10.1186/s40462-020-00226-6


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.

WaderTales wins BTO Award

I am using this brief WaderTales blog to say ‘thank you’ to the BTO for kindly presenting me with the 2020 Dilys Breese Medal, in recognition of the role that WaderTales plays in the dissemination of BTO science relating to waders. Some of these blogs are listed below.

Receiving the Dilys Breese Medal is very special. It’s an honour to follow previous recipients such as Chris Packham and Michael McCarthy but it’s more personal than that.

Before I worked for BTO I was a Council member of the Trust for several years, at a time when Dilys Breese was also a Trustee. Later, during my time as a member of BTO staff, Dilys continued to be an active Council and working group member, culminating in her role as Hon. Secretary (1998-2001).

In 2007, Dilys died and we learnt that the BTO was to receive a significant legacy which was subsequently used to reinvigorate nest recording.  Paul Reddish, who was acting as Executor, and I wanted to make sure that Dilys would be remembered beyond the end of her gift. With this aim in mind, BTO created the Dilys Breese Medal, awarding the first six medals in 2009 and one a year thereafter.

Dilys Breese

Few people who are reading this will have known Dilys Breese but they will recognise her through her TV productions, especially her work for the BBC Natural History Unit. She created the Living World and Wildlife series for the BBC, before leaving the Corporation in 1991 and setting up Kestrel Productions. Her 1987 Meerkats United programme, with David Attenborough, is probably her most famous programme but there were many more highlights over a distinguished radio and TV career.

Dilys became a BTO member in 1973, bringing many BBC and Kestrel films to annual conferences, working with Chris Mead and others to increase the profile of the Trust and playing an active role in the charity’s governance. Dilys Breese fervently believed that nature and science should be shared with as many people as possible and I am happy to play my part in doing just that.

WaderTales and the BTO

WaderTales blogs that are about BTO-led research and surveys have included:

BTO staff are involved in a study of breeding Curlew in Breckland
  • Why are we losing our large waders? The BTO’s Director of Science, James Pearce-Higgins, is lead author of a review of the problems facing all of the curlews and godwits of the world
  • Curlews can’t wait for a treatment plan. Sam Franks is lead author of a joint BTO/RSPB review that helped to establish the key gaps in our knowledge of problems faced by Curlew, setting the direction for Curlew conservation science and interventions.
  • Do population estimates matter? This blog summarises the ‘waders’ section of the population estimates paper in British Birds, based on data from the Wetland Bird Survey.
  • 25 years of wader declines is a nice example of long-term survey work by Mike Bell, a BTO volunteer and Regional Representative, written up with John Calladine of BTO Scotland.

The Dilys Breese medal

The Dilys Brees Medal was designed by Norfolk artist Robert Gillmor. It features a Robin, the subject of a book that Dilys was working on at the time of her death, set against the outline of an old fashioned TV screen. This will be a lovely memento of fifteen years of working with Dilys to promote the work of the BTO. I am grateful to Mary Colwell (author of Curlew Moon) who kindly nominated me for the award.

Graham Appleton

Click HERE to see more blogs from the first five years of WaderTales