Spoon-billed Sandpipers: Track and Trace

The cutest wader in the world has to be the ‘critically endangered’ Spoon-billed Sandpiper, a tiny wader with an ice-cream spoon for a bill. An ever-reducing number of pairs breed in the coastal tundra of north-east Russia. They migrate to south-east Asia, spending the winter months anywhere between China and Bangladesh.

During autumn there are sightings of moulting Spoon-billed Sandpipers around the mudflats of the Yellow Sea (People’s Republic of China, Democratic People’s Republic of Korea (DPRK) and Republic of Korea). Where else do Spoon-billed Sandpipers go? A new paper shows that it is possible to trace potentially important missing sites by tracking individuals.

Away from their breeding areas, Spoon-billed Sandpipers are threatened by:

  • Loss of non-breeding habitats, especially intertidal mudflats, because of land-claim projects to create harbours, industry zones, wind and solar power generation farms, aquaculture ponds and rice-fields.
  • The spread of invasive Spartina species (cordgrass) across mudflats in some coastal areas of China, the Republic of Korea and Japan is reducing the available feeding area.
  • Local hunting pressure, for personal consumption and local trade.
  • Accidental losses of birds tangled in permanently set fishing nets.

There is more about these issues and efforts to reduce problems being faced by waders on the East Asian-Australasian Flyway on the Saving the Spoon-billed Sandpiper website.

Better information on the location and timing of use of stopover and wintering sites is essential if conservation measures to prevent hunting and further losses of intertidal habitat are to be applied across the species’ range. In a new paper in Wader Study, Prof Qing Chang and colleagues describe in detail the post-breeding migration of adult Spoon-billed Sandpipers. For the first time, they are able to report on the timing of the migration, the duration of stay at stop-over sites, and the distances travelled between stop-overs.

Six Spoon-billed Sandpipers were caught in Chukotka

The research team captured 13 adult Spoon-billed Sandpipers and fitted each bird with a solar-powered transmitter that reports the bird’s locations, via satellites. Six were caught on their nests in Chukotka and seven were netted at Tiaozini in Jiangsu Province, near Shanghai in China. The paper contains full information on the tags, which were glue-mounted to the back of the birds, and details of the data collected and the algorithms used to interpret groupings of locations. This will be of help to anyone considering using these devices.

Why use Satellite transmitters?

Information from colour-ringing and counting has produced fascinating information about Spoon-billed Sandpipers. We now know more about the breeding, migration and wintering locations of the total population, estimated at just 660 individuals in 2014, than we did in 2010, when the serious plight of the species became more widely apparent (Clark et al). There has been international support for conservation action in non-breeding hot-spots in Myanmar, Bangladesh and China, where waders are benefiting from measures designed to reduce hunting pressure and maintain feeding habitat.

Counting waders in the Gulf of Mottomar in Myanmar

The amount of information that can be obtained from counts and colour-ring sightings is limited by knowledge of where to look for birds. There are still big questions to ask. Where do birds colour-ringed in Russia, but not yet seen, spend the winter, where are the breeding grounds for birds ringed in the winter and then not seen in the summer, and what happens to birds in the weeks when they are on migration? Geolocators or satellite transmitters might provide some answers.

Geolocators are great, but information can only be downloaded from these devices by recapturing tagged birds and there is poor precision of reports received during the equinox periods (late March and late September), when daylength doesn’t change with latitude and many waders are on the move. Additionally, given the tiny size of the population and the mobility of breeding birds, recapturing birds to remove geolocators is unlikely to be as easy as it has been for many other wader species. Finally, as has been discussed in a previous WaderTales blog, geolocators can have unanticipated negative consequences for small calidrid sandpipers.

Health & Safety

Every Spoon-billed Sandpiper is precious, so safety is of paramount importance in tagging studies. Prior to deployment on Spoon-billed Sandpipers, tags of the same weight and dimensions were trialled on ‘surrogate’ birds – a small flock of twelve captive-reared Dunlin. The health of these birds was monitored in an aviary and birds seemed to behave normally. Would the same be true for similarly-sized Spoon-billed Sandpipers that migrate thousands of kilometres? Imagine the relief when the first tagged wild bird took off a few days after tagging and started to reveal unique insights into the species’ migration!

From Russia with tags

The six adults captured on the nest and tagged in subarctic Chukotka, Russia, left in July and moved west and south through Kamchatka in July and early August. This was followed by long flights (>1,000 km) across the Sea of Okhotsk to Sakhalin Island. By this stage, only four of the tags were still functioning but these birds provided some fascinating information:

  • All four birds used the same area (Tyk Bay) on the western side of Sakhalin Island. They stayed for long periods and all flew long distances when they left – which means that this site and the resources it provides are really important!
  • The next leg of the journey took the birds further south to sites within Russia and to the Democratic People’s Republic of Korea. All four ended up in DPRK.
  • Two birds stayed long enough to moult close to the Demilitarised Zone in the DPRK but the other two moved on and spent a month moulting at two different sites in Jiangsu Province, China.
  • By this point, in the late autumn, it is believed that all four birds had moulted. Given the method of tag attachment, it was thought that birds would drop their tags during moult, but one bird (L07) continued to transmit data.
  • The four individuals that were tracked between the breeding area and their presumed moulting sites stopped for 2 days or more at between 3 and 7 sites.

Post-moult migration

Seven birds were tagged in Tiaozini in Jiangsu Province. With L07 still transmitting, that meant that there were eight birds to track during the next stage of the migration season. Would they be able to trace missing sites that could potentially be protected.

  • All eight of these birds moved west and south in October or early November.
  • Three birds moved to separate sites in southern China, where they remained until their tags ceased to provide data.
  • Five birds visited stopover sites in China before moving on to their wintering areas in Vietnam, Myanmar, Sumatra and Bangladesh. Sumatra is outside the previously-known wintering range.
  • One of the birds that flew to Bangladesh stopped in Vietnam and Myanmar, while the other one stopped in the Gulf of Thailand. It then overflew Malaysia, Myanmar and the Bay of Bengal before transmissions ceased just before arrival in Bangladesh.
  • The eight individuals that were tracked between moulting and wintering grounds trace out a vast coastline (figure) – illustrating the conservation challenges of trying to save the Spoon-billed Sandpiper. Only two of the birds finished up at well-known sites that are covered regularly by winter counts.

Identifying sites of conservation importance

With only thirteen tagged birds providing four links between breeding and moulting areas and eight links between moulting and wintering areas, the research team have greatly increased our understanding of how it might be possible to protect Spoon-billed Sandpipers. As the authors point out in their Discussion, however, the “list of stopover sites is not comprehensive because of the small number of birds tagged and the duration of stay criterion we used”. Seventeen sites were visited by only one bird and other sites where Spoon-billed Sandpipers are regularly seen were not visited by any of the tagged birds. This suggests that there are probably other important sites that are yet to be traced. The authors suggest some of the limitations created by sampling. The key findings are:

  • During the post-breeding migration, several sites appeared to be of special importance. Seven stop-over sites were used for long periods or were used by birds immediately before long flights (or both).
  • Tyk Bay (Sakhalin, Russia) and Ryongmae Mudflat (DPRK) were used as stopovers by all the tagged birds that passed beyond these sites. Neither site was previously thought to be important for Spoon-billed Sandpipers.
  • The post-breeding moult period is an energetically expensive stage of a wader’s annual cycle. For Spoon-billed Sandpipers, Ryongmae Mudflat (DPRK), Tiaozini (China) and Yangkou (China) are of special importance in this regard (Green et al. 2018, Chang et al. 2019, Yang et al. 2020).
  • Most of the sites in which tagged birds spent the winter months had not previously been visited by count teams. Subsequent visits to some of these previously unknown sites in China added counts of 77 birds.

Once tags had fallen off, birds could still be located by their leg-flags if they were seen by teams of observers who visited known moulting, stop-over and wintering locations. Seven of the birds that carried transmitters have been seen in subsequent years at similar times and places. This suggests that birds are site-faithful between years, implying that a site that is identified to be of importance is really important – birds are not randomly choosing mudflats on a whim.

Yellow 57 – also known as Y57

The stopover-site clusters of registrations were all located on or near coasts, except for one, used briefly, on sandbanks in the Irrawaddy River, Myanmar. Most clusters included areas of intertidal mudflats, especially on estuaries. However, a few included other habitats, such as saltpans and fishponds in impounded areas which had previously been intertidal. Ten of the 28 clusters have some protection under national legislation or international agreements, a further eleven clusters are recognised as Key Biodiversity Areas and/or East Asian-Australasian Flyway Network Sites, but seven clusters appear to have neither protection nor international recognition.

The lack of protection of wintering sites is of concern because of continuing threats to Spoon-billed Sandpipers and their habitats. Hunting of Spoon-billed Sandpipers remains a problem, for instance. This is illustrated by a story from the paper.

During a visit to site Guankoudu (Fujian Province, China) in December 2016, occasioned by the tracking of one of the tagged birds, many mist-nets, more than 2 km in total length, were found, some of which held entangled live and dead shorebirds. This site has no legal protection, but this illegal bird-trapping was reported to local government agencies, whose staff quickly began the removal and destruction of the nets.

If sites are identified, protection is possible.

There may be a Spoon-billed Sandpiper in this cloud of waders over the Taiozini Mudflat

Background to this work on Spoon-billed Sandpipers

The Spoon-billed Sandpiper conservation programme, which includes research, site protection, conservation breeding and head-starting, is a collaboration between the Wildlife & Wetlands Trust (WWT), Birds Russia, Moscow Zoo and the RSPB, working with colleagues from the BTO, BirdLife International, ArcCona, Nanjing Normal University, Spoon-billed Sandpiper in China, Hong Kong Waterbirds Ringing Group, Microwave Telemetry and the Spoon-Billed Sandpiper Task Force.

The project is supported by WWT, RSPB, the UK Government’s Darwin Initiative and SOS – Save our Species, with additional financial contributions and support from BirdLife International, the East-Asian Australasian Flyway Partnership, the Convention on Migratory Species, Heritage Expeditions, the Australasian Wader Study Group of Birds Australia, the BBC Wildlife Fund, Avios, the Olive Herbert Charitable Trust, the Oriental Bird Club, British Airways Communities & Conservation Scheme, New Zealand Department of Conservation, the Queensland Wader Study Group, New South Wales Wader Study Group, Chester Zoo, Wader Quest, Dutch Birding, OSME and British Birds Charitable Trust and many generous individuals. Leica Camera AG is WWT’s exclusive optic partner for this key conservation project.

An assessment of the conservation status of the species can be found on the BirdLife International site:

To read more about the project to set up a captive breeding population and head-start Spoon-billed Sandpiper chicks in their Russian breeding grounds visit the Saving Spoon-billed Sandpiper website.

There is lots of information on the conservation action to protect the species on the Saving the Spoonbill Sandpiper website and on the East Asian-Australasian Flyway Partnership Website. Here’s one example.

Many wader species on the East Asian-Australasian Flyway are threatened by habitat loss, as discussed in this WaderTales blog.

Paper in Wader Study

Post-breeding migration of adult Spoon-billed Sandpipers Qing Chang, Evgeny E. Syroechkovskiy, Guy Q.A. Anderson, Pyae-Phyo Aung, Alison E. Beresford, Kane Brides, Sayam U. Chowdhury, Nigel A. Clark, Jacquie A. Clark, Paul Howey, Baz Hughes, Paul Insua-Cao, Yifei Jia, Elena Lappo, Katherine K.S. Leung, Egor Y. Loktionov, Jonathan Martinez, David S. Melville, James Phillips, Chairunas Adha Putra, Pavel S. Tomkovich, Ewan Weston, Jenny Weston, Nikolay Yakushev & Rhys E. Green. Wader Study 127(3): doi:10.18194/ws.00201


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.

The First Five Years

This article celebrates five years of WaderTales. It highlights some of the most well-read tales and picks out a few cross-cutting themes. It has not been possible to include links to all of the 98 WaderTales blogs but you can see them all by clicking HERE.

There are six sections:

  • The most popular stories
  • It all started in Iceland
  • Migration
  • A focus on individuals
  • Thoughts about moult (moult)
  • Conservation issues

The most popular stories

Five blogs on WaderTales have been downloaded 3500 or more times, with the most popular one registering over 10,000 reads. The top five are:

It all started in Iceland

The first WaderTales blog, How volcanic eruptions help waders, was published on 28 September 2015. It explains how the distribution of breeding waders in Iceland is linked to the amount of historical volcanic activity, with ash acting as fertilizer in the central parts of the country. Several other Icelandic studies focus on the ways in which species such as Redshank have taken advantage of opportunities that are provided by farmers’ fields and a warming climate. Designing wader landscapes investigates whether Iceland’s high breeding densities can be maintained, as farming expands and intensification increases.

Migration

Unsurprisingly, migration is a recurring theme in WaderTales. Some of my favourite migration stories are:

  • Which Icelandic Oystercatchers cross the Atlantic? Great teamwork by scientists and colour-ring readers has helped to work out which of Iceland’s Oystercatchers leave Iceland. 70% of birds migrate to Ireland, the UK and western coasts of mainland Europe but 30% ‘tough it out’ in Iceland.
  • Plovers from the north is about Grey or Black-bellied Plovers, a much under-studied wader that travels from the tundra to countries as far south as Australia, Chile and South Africa.
  • Well-travelled Ringed Plovers is an amazing migration story, linking Egypt and Somalia to Chukotka, in the northeast corner of Russia. Here, Ringed Plovers from Africa meet Knot from Australia and Buff-breasted Sandpipers from Brazil.
  • Iceland to Africa, non-stop is about a paper that changed our understanding of the migration of Whimbrel, when geolocators revealed that birds head straight across the Atlantic, on their journeys south. Other Whimbrel blogs talk about the timing of migration and the weather cues associated with decisions made by individuals.
  • Overtaking on migration reveals that Black-tailed Godwits that spend the winter in Portugal, at the southern edge of the species’ wintering range, still get back to Iceland earlier than birds that only have to travel half as far.
  • Teenage waders introducess a previously unknown site in Argentina that is used by non-breeding Hudsonian Godwits in the austral winter. When adults fly north from Chile to Alaska, young birds head inland to the Pampa wetlands. What other habitats do slow-maturing and threatened wader species depend upon?

A focus on individuals

The use of colour-rings, geolocators and satellite tracking has helped to turn the spotlight on individual birds, such as the Greenshank alongside, instead of the patterns we see across populations.

Why is spring migration getting earlier? This early blog focuses on spring arrival dates of Black-tailed Godwits in Iceland. Although the migration season is advancing, individual birds are not changing their annual timetables. Pioneering, new recruits are on earlier schedules than previous generations.

Travel advice for Sanderling introduces the concept of ‘happenstance’ to WaderTales. Colour-ring sightings have shown that Sanderlings from the same breeding areas of Greenland can end up in non-breeding locations that can be anywhere between Scotland and South Africa. Some birds settle in equatorial countries, where the apparent annual survival is lower, from which fewer young birds return to Greenland to breed in their first breeding season, and where it is less likely that an individual will be able to end up on an early breeding schedule. Interestingly, survival rates appear similar in Scotland and Namibia, despite the huge difference in the distance from Greenland. The ‘dice are rolled’ and an individual can end up in a good or poor site, to which it will return every year.

Generational change. In a changing world, with more chaotic weather patterns and rapidly altering habitats, migratory birds are faced with opportunities and challenges. Long-term monitoring of Black-tailed Godwits has shown that migration patterns are forged by new generations, the behaviours of which are moulded by the conditions they encounter in early life.

Thoughts about moult

The main moult of northern hemisphere waders typically happens in the late summer, when the breeding season has finished and once birds have left the breeding grounds. There is then another moult before the start of the next breeding season, as birds change into summer finery (and can change the way they smell). These two moult periods may take up as much as a third of a shorebird’s year but do not get very much attention in scientific studies.

Conservation issues

A lot of the papers that are described above are based upon research that focuses upon species that are of conservation concern. This final selection of blogs highlights a few cross-cutting conservation themes.

Acknowledgements

The purpose of the blog series has not changed since I wrote this introduction on 24 September 2015, but the range of species and the geographic scope have both increased over the years.

WaderTales blogs are used to celebrate waders and wader research. Many of the articles will be based on previously published papers, with the aim of making wader science available to a broader audience. The choice of topics will reflect personal interests, so there will be plenty about Black-tailed Godwits and the international team of scientists who study their behaviours and life-histories. I hope that these blogs will be of particular interest to the hundreds of people who contribute their sightings of colour-ringed Black-tailed Godwits to the ever-expanding database of movements.

There are 98 blogs in the WaderTales catalogue but WordPress tells me that there have actually been 109 posts. The extra eleven represent summaries at the end of each year and occasional syntheses of articles that cover a particular topic, such as migration blogs on wadertales and Wetland Bird Survey: working for waders.

It is humbling to discover that 118,000 people have visited WaderTales in the first five years, however briefly some of them may have stopped by.

I am grateful to all of the authors who have worked with me to make sure that WaderTales blogs properly represent the findings of their research, to the photographers who generously permit free use of their images and to my wife, Professor Jennifer Gill, who encourages and inspires me. It is no surprise that Black-tailed Godwits appear in more blogs than any other species!

There seems to be no shortage of new shorebird research to write about. If you have ideas of topics I should cover or you have an upcoming paper that might turn into an interesting WaderTales blog, please get in touch. A blog works best if I can work up a story in time to share it with the lead author and publish it alongside a paper. Here’s to the next five years!

Graham Appleton

Here’s a link to the full WaderTales catalogue

Coming soon

28th September marks the fifth anniversary of WaderTales. I am working on a blog that highlights some of the most popular blogs and some of my personal favourites but I am having some technical issues. While I continue to struggle, here is a blog that points to over twenty articles about migration:

CLICK HERE FOR BLOGS ABOUT MIGRATION

The most popular stories

Five blogs on WaderTales have been downloaded 3500 or more times, with the most popular one registering over 10,000 reads. The top five are:

‘The First Five Years’ will hopefully be published shortly

Flagging up potential problems

Any device that is added to a bird (or other animal) has the potential to affect the way it behaves. Even something as simple as a metal ring could increase risk, if it is fitted incorrectly or if fishing line gets caught around it, for instance.

In a 2020 paper in Bird Study, Thomas Mondain-Monval and colleagues report on the way that differently mounted geolocators affect Common Sandpipers. These devices were being used to help understand the migratory behaviour of the species, part of a Lancaster University PhD project that aims to explain a rapid decline in breeding numbers in England.

Safety first

Any researcher who uses rings, colour-rings, tags or tracking devices to study waders needs to ask (and answer) the following four questions:

  1. Is there a good reason to use the device? What’s the question and will the results be analysed and published?
  2. Is the device being fitted as safely as possible? Has it been used on similar species and what happened?
  3. How do the birds react to the device? If trying something new, perhaps the device can be trialled on captive birds.
  4. Are there any differences between birds wearing different types of rings or devices? Write up your results so as to help future researchers.

Thomas and his colleagues have followed this process through to its conclusion by writing a paper that is published in Bird Study. In it, they compare return rates for Common Sandpipers wearing rings and geolocators and detail a number of injuries that could potentially be linked to the geolocators.

Ringing a Common Sandpiper, before adding a colour ring and a flag

Common Sandpipers

The latest Breeding Bird Survey data suggest that numbers of breeding Common Sandpiper dropped by 40% in England and 24% in Scotland between 1995 and 2018. Over the longer period covered by the three BTO-led breeding Atlases (1968-1972, 1988-1991, 2008-2011) there have been losses from the edge of the species’ range, suggesting that decreases were already under way before the start of BBS recording period (see map). Common Sandpiper was added to the Birds of Conservation concern amber list in 2009. There are insufficient data from the BTO Nest Record Scheme to work out whether declines may be linked to breeding success.

Common Sandpipers in the River Lune study area nest close to running water

The European population of Common Sandpiper has seen a widespread, moderate decline since 1980, indicating that there may be large-scale drivers of losses. Is something going wrong in the non-breeding grounds? Previous geolocator studies have shown that Common Sandpipers rely upon a series of stopover sites on migration (see Not-so-Common Sandpipers) and it is possible that these are declining in quantity and/or quality.

As part of his Lancaster University PhD, Thomas Mondain-Monval’s PhD took a two-pronged approach to an investigation of migration routes. He added geolocators to flags on birds in both England and Senegal. The fact that different tags were used in the two countries enabled him to compare the tag effects on study birds. He was also able to compare tagged birds to a sample of colour-ringed birds.

The study systems

UK fieldwork was carried out in the River Lune catchment area in Cumbria, a northern county of England, as part of a detailed study of 24 breeding pairs. Unmarked adults were caught each year and fitted with a BTO metal ring, a yellow colour-ring (engraved with two unique black characters) and a plain red ring or flag. Similar colour rings were used on Common Sandpipers that were caught on their wintering grounds in Djoudj National Bird Sanctuary, Senegal.

Red flags were used on birds that carried geolocators as these provided space to affix the device. This sample consisted of 22 individuals in the UK and 10 individuals in Senegal. The control samples of birds with colour- rings but no geolocators were 28 individuals in the UK and 6 individuals in Senegal. Dimensions of flags and geolocators are provided in the paper, together with information on methods of attachment. The combined mass of the geolocator, flag and glue was 1.1 g for the birds ringed in England and 1.0 g for the Senegal birds, which is about 2% of body mass of the 50 g Common Sandpipers. The Senegal tags were slightly lighter but a little longer. See paper for details.

Mist nets, drop traps and whoosh nets were used to catch Common Sandpipers that were wintering in the Djoudj National Bird Sanctuary in Senegal

The Common Sandpipers in the UK were observed at least weekly throughout the breeding season. Tagged birds wintering in Senegal remained site-faithful and were observed opportunistically, usually weekly for up to five weeks following capture. It is unusual for researchers to be able to monitor the behaviour of tagged birds as closely as was the case here. When it became apparent that two birds belonging to the breeding study had started to limp, attempts were made to catch the birds. One bird was retrapped and the orientation of the geolocator was changed from parallel to the leg to along the line of the tag. This bird stopped limping and the parallel orientation was not used again.

Flag & geolocator effects

Common Sandpiper in Senegal, wearing a flag-mounted geolocator

The key measures of success that are usually monitored by researchers indicated no difference between birds with and without geolocators:  

  1. For the English, breeding population, there were no significant differences between the return rates or return dates of birds with geolocators and those without.
  2. There were no significant differences in hatching success or fledging success between birds with and without geolocators in either 2017 or 2018, although sample sizes were small.
  3. There was no significant difference in condition between birds with and without geolocators.

Most researchers who deploy geolocators on waders are using them to collect a year’s worth of data from their study birds. Typically, a bird is caught on its nest in one year and then caught again a year later – which might sound easy but isn’t! The fact that Thomas was also studying his small population in detail provided extra opportunities to collect information which should be helpful to others. Although there were no detectable effects of geolocators, as assessed using the metrics described above, a small number of individuals tagged in the UK experienced injuries:

  1. One of the birds that had been fitted with a parallel-mounted geolocator sustained an injury to its lower leg, possibly due to a constriction of blood flow. The bird was still able to continue with its breeding attempt.
  2. On their recapture in 2018, two of the seven birds carrying parallel-mounted geolocators were noted to have bruising on the tarsus, apparently caused by the geolocator hitting the lower leg whilst the bird was walking.
  3. In five cases, individuals had a slightly swollen tibia or had lost some skin underneath the leg flag. This occurred irrespective of tag orientation and appeared to be caused by the internal diameter being marginally too small for the individual, although no rubbing was noted and all flags rotated freely at the time of fitting.
  4. In Senegal, no injuries were seen on any of the tagged birds. These birds were wearing similar flags but carried lighter geolocators than the English birds.

The research team concluded that injuries to the legs of some of the study birds were caused by carrying geolocators. They suggest that they were probably due to a combination of geolocator size and weight, and the short tibias of Common Sandpipers. Mounting long geolocators parallel to the leg on species with short tibias may impede leg movement. When the team switched to thinner and lighter tags for their work in Senegal there were no problems.

It is good that Thomas and his colleagues have published the information about the issues associated with the original tagging method that they used, so that others can learn from their experiences. Had they simply reported return rates and measures of reproductive success their results would have suggested that geolocators had no negative effect on these Common Sandpipers. It would have been easy to miss out the extra detail about the small risk of leg injury.

Bird ringers are always aiming to improve catching, handling and tagging techniques. Within the UK, the use of flag-mounted or harness-mounted geolocators requires project-by-project approval from the BTO’s Special Marks Technical Panel. Annual reporting enables the SMTP to update guidance for other researchers.

Refining the way that flags are used

Flags have been used on waders for over forty years and only occasionally have birds seemed discomforted by being asked to wear them. This seems more likely to happen if the flag is applied to the upper part of the leg. When occasional individuals are observed leg-flicking it may be because the ring sits awkwardly on the tibia-tarsal joint. The flick is thought to rotate the flag into a more comfortable position. Nigel Clark, who affixed his first flag to a Dunlin in 1978 suggests the following remedies:

  1. It goes without saying that the edges of all colour-rings and flags should be sanded to remove sharp edges.
  2. Flags are heavier than colour-rings and this means that they sit more firmly on the tibia-tarsal joint, at a point which is wider in diameter than that of the rest of the tibia. When making flags the internal diameter may need to be slightly larger than that used for colour-rings on the same species.
  3. The addition of a geolocator further increases the mass of the flag. When there were concerns about flag-mounted geolocators in North America, Ron Porter solved the problem by making sure that there was a colour-ring underneath the flag. The ring rotates easily, acting as a ‘washer’ between the tibia-tarsal joint and the flag.
  4. When a wader is very thin, as it may be after a long flight, the diameter of the leg can sometimes be less than expected for the species. In Spoon-billed Sandpipers, where there is only space for one ring on the tibia, flagged birds have occasionally been seen leg-flicking. When the leg-flags were modified, to reduce the internal diameter, things improved.

If there is a paper that describes or expands upon the above list, I shall be delighted to add a reference.

To learn more

This blog focuses on a 2020 paper in Bird Study, the journal of the British Trust for Ornithology:

The effects of geolocators on return rates, condition and breeding success in Common Sandpipers. Thomas O. Mondain-Monval, Richard du Feu and Stuart P. Sharp

Three previous WaderTales blogs have discussed issues relating to flags and geolocators:


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.

Teenage waders

Hudsonian Godwit in breeding plumage

A paper by Juan Navedo & Jorge Ruiz, focusing on Hudsonian Godwits, raises important points about the conservation of the world’s larger shorebirds.

Many curlews and godwits don’t breed in their first year but what do they do instead and how quickly do individuals recruit into the breeding population? These answers have direct implications for the conservation of these species, numbers of which are declining in most cases.

Hudsonian Godwits

Hudsonian Godwits breed in Alaska and Canada and spend the non-breeding season in Chile and Argentina. There are three well-separated breeding populations; in south-central and western Alaska, along the northwest coast of Canada (Mackenzie and Anderson river deltas) and within the Hudson and James Bay region of northern Canada. These are indicated in the figure alongside, based on the map from BirdLife International’s datazone.

On migration, Hudsonian Godwits do not use coastal areas, which led to the theory that their journeys north and south might be made without a break. Satellite tracking has revealed that staging areas are continental rather than coastal. The latest research shows that birds wintering in Chile stop off in the prairies of North America on the way north. On the return journey, there are key refuelling areas in Saskatchewan (Canada) and in continental wetlands between Colombia and Argentina. Map below is from a paper from Senner et al.

Satellite tracking of two birds from the Mackenzie Delta breeding population, on Canada’s Arctic coast, revealed a 1500 mile two-day ‘hop’ to Hudson Bay, a long refuelling and moulting period and then a 4 or 5 day direct flight to South America. These are very impressive migrants!

As discussed in Why are we losing our large waders?, the Hudsonian Godwit is still considered to be of ‘least concern’ on the IUCN/BirdLife list. The fact that the species breeds over a broad sweep of Alaska and Canada, even if in discrete areas, and that the population, estimated to be 77,000 individuals (Andres et al 2012), is well over the 10,000 cut-off for threat consideration, means that the species is not yet designated as being of international concern. In Canada, Hudsonian Godwit was added to the ‘threatened species’ list in 2019, as a consequence of reduced breeding success and a major decline in the Canadian breeding population. The latest population estimate in the COSEWIC report is that there are just 41,000 mature individuals (24,300 in the Hudson Bay Lowlands, 800 in the Mackenzie Delta, and 15,750 in Alaska).

Non-breeding youngsters

Releasing a satellite-tagged Hudsonian Godwit

When Hudsonian Godwits depart from the coasts of Chile and Argentina, on their way to Alaska and Canada, they leave behind young birds that will not breed in their first year – and possibly even the second or third. These sub-adults are the future of Hudsonian Godwit conservation. In a declining population, it is important that as many as possible of these youngsters will reach maturity and breed successfully.

Juan Navedo, Jorge Ruiz and colleagues from Universidad Austral de Chile, have been studying the ecology and migratory behaviour of Hudsonian Godwits that winter in Chiloé Island (c. 32°S, Chile) as summarised here. One of the unexpected outcomes of this work is a 2020 paper in Global Ecology and Conservation, entitled Oversummering in the southern hemisphere by long-distance migratory shorebirds calls for reappraisal of wetland conservation policies. In it, they followed the movements of a small number of satellite-tagged adults and discovered significant flocks of non-breeding birds. Their great detective work has clear implications for the potential recovery of Hudsonian Godwit populations and wider consequences for other species of shorebirds that don’t breed in their early year or years of life.

Spring departure

Hudsonian Godwits in Chile are being tracked to improve understanding of the connectivity between their discrete breeding areas and their wintering areas. Tracing their journeys also helps to establish the refuelling areas that are used during northwards and southwards migration.

When it was time to depart from Chiloé Island in spring, most adult Hudsonian Godwits spent a week flying north non-stop over the Pacific, crossed Mexico and staged in the plains of North America but, in 2017, three tagged birds unexpectedly headed northeast to the Pampa wetlands of Argentina. These birds all remained in the Pampa area for five or more months. Their tags provided positions every thirty minutes, supplying the scientists with the information they needed to identify key ‘oversummering’ areas for the species. By focusing on groups of locations for two of the tagged birds, it was possible to identify a 28,000 km2 area that seemed to be of particular importance. Was this where young Hudsonian Godwits (not wearing tags) spent the same period?

The paper explains how the team searched the vast area of permanent and ephemeral wetlands in a systematic way, allowing estimates to be made of the number of shorebirds of a range of species that spend time in this area, instead of migrating north to breed. Hudsonian Godwits were found in four (out of 44) wetlands in 2018 and three in 2019, making a total of 366 and 746 individuals in the two years.

Looking for Hudsonian Godwits in the Pampa Wetlands of Argentina

In their three-day surveys, the team was only able to survey a small number of potential feeding sites within the vast area. On the assumption that Hudsonian Godwits mature at the same rate as other large, long-distance migrant waders, such as limosa Black-tailed Godwits and baueri Bar-tailed Godwits, Juan Navedo and Jorge Ruiz suggest that nearly half of first-year, a quarter of second-year and 15% of third-year Hudsonian Godwits may be using these continental wetlands during a crucial stage of their lives. Numbers of Lesser Yellowlegs and Greater Yellowlegs that they found in the same habitats were also of conservation significance, and the Pampa wetlands are also a ‘summering’ area for Buff-breasted Sandpiper and Upland Sandpiper.

Conservation implications for Hudsonian Godwits

Young Hudsonian Godwits will hopefully breed in Alaska in later years

The paper by Juan Navedo & Jorge Ruiz clearly demonstrates the significance of the Pampa wetlands for waders that were raised in the Northern Hemisphere but which don’t return there until their second, third or even fourth potential breeding season. What is it about these wetlands that is so important to young Hudsonian Godwits, how vulnerable are they and what other inland areas are being used by flocks of young birds? The authors point out that the pampas habitats of Argentina are changing. The Pampa wetlands are being turned into vast swaths of agricultural land, much of which is being planted with herbicide-resistant transgenic soybean. Globally, it is estimated that over 90% of soybean is grown to supply animal feed. This is a thirsty crop that requires irrigation, sucking water out of the remaining wetlands. These grassland habitats are subject to a Memorandum of Understanding on the Conservation of Southern South American Migratory Grassland Bird Species and Their Habitats.

Flagged Hudsonian Godwit

The presence of some adult birds in the Pampa wetlands flocks is not surprising. As discussed and referenced in the paper, individuals that migrate long distances and that are on tight schedules may need to skip the occasional breeding season if they do not have sufficient fat reserves to head north on schedule. When studying tracked individuals of migratory shorebirds that undertake long, non-stop flights, it has been shown that birds occasionally abort their journeys if they encounter adverse weather conditions. We know that godwits of other species can live for thirty years or more so there is always next year.

Wider implications

The Hudsonian Godwit paper is not just about one species. It asks important questions about the conservation of waders and other families of birds that do not breed in their first year. Globally, have we identified the most important shorebird sites, can we protect them from development and are some sites more important than others? Do we pay these sites enough attention in the breeding season, when the large swirling flocks have departed, leaving much smaller aggregations of non-breeding birds sparsely distributesd throughout flyways? Protecting these small oversummering flocks is investing in the future of threatened wader species.

Site protection: This paper has highlighted an important issue. What do young curlews, godwits and other large and medium-sized waders do in the ‘teenage’ years – that important period between being a juvenile and being a breeding adult? Where are they? Are the sites protected? Do birds simply stay in the areas in which they settle in August, September or October, after they have flown south from the breeding grounds? The Pampa wetlands of Argentina are unlikely to be the only non-coastal areas that are used by young waders; what other sites are we missing? For Hudsonian Godwits, perhaps there needs to be a broader definition of key shorebird areas when considering candidate sites that need to be protected as part of the excellent Western Hemisphere Shorebird Reserve Network? More broadly, the authors propose that conservation agreements regarding wetlands of international concern should include a specific criterion for oversummering areas.

Figure illustrating delayed maturity of Hudsonian Godwits (from Navedo & Ruiz)

Youth clubs: Young waders recruit to the breeding population at different ages. If the typical life expectancy of a godwit is ten years then a bird that flies north in its second summer will, on average, produce 12% more chicks in its life-time than one that does not breed until a year later. Hudsonian Godwits not only need to survive in these Pampa youth clubs, they also need to thrive.

Within the same species, time of first breeding can be influenced by the non-breeding site than an individual happens to use. In their fascinating paper about Sanderling migration, summarised in the WaderTales blog Travel advice for Sanderling, Jeroen Reneerkens and colleagues showed large difference in the proportion of young birds that travelled north in the first summer. Most Sanderling that spend the winter in England and Portugal fly to Greenland in spring but only a tiny proportion of birds wintering in Ghana have this extra breeding attempt. They link these differences to site quality.

Eurasian Curlew and a young Black-tailed Godwit

Disturbance: When the number of Eurasian Curlew on a British or Irish estuary drops rapidly, in March and April, and when adult Far Eastern Curlew leave Australia to head for eastern Russia, do we pay enough attention to the small number of birds that remain?

In the northern hemisphere, in particular, the summer months of May through to July bring increased disturbance pressure to beaches and to estuaries, at a time when non-breeding waders are trying to find the resources they need to undertake their primary moult. Perhaps more thought needs to be given to zoning recreational activities in areas which are internationally designated as conservation areas? A May count of 27 Eurasian Curlew on the Exe Estuary in Devon may seem trivial, when compared to 849 in August (Wetland Bird Survey 2018), but these birds represent the future.

In summary

As Juan Navedo & Jorge Ruizwrite in the abstract of their paper:

Given their delayed maturity, many long-distance migratory shorebirds may spend large portions of their lives in previously undocumented wetlands, while deferring migration. These unrecognized oversummering habitats fall outside the scope of today’s conservation efforts for Hudsonian Godwits, because they are not spatially nested within the non-breeding grounds, an issue to be studied for other shorebirds.

We are seeing rapid declines of many of the Numeniini family (see this blog about curlews, godwits and Upland Sandpiper) and other slow-maturing shorebird species, and ‘teenage birds’ deserve more attention. We have to identify the areas used by immature birds as quickly as possible, before productivity is so low that we cannot find them.

Oversummering in the southern hemisphere by long-distance migratory shorebirds calls for reappraisal of wetland conservation policies. Juan G. Navedo & Jorge Ruiz. Global Ecology and Conservation doi.org/10.1016/j.gecco.2020.e01189

Wintering Hudsonian Godwits on Chiloé Island, Chile.

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

Cycling for waders

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

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

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

Quick reminder of head-starting

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

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

International Wader Study Group (IWSG)

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

Mark and Jen

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

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

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

Latest news from Project Godwit

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

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

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

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

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

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

Conservation challenges

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

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

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

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

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

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

Support for Mark and Jen

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

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

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


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

Trees, predators and breeding waders

When trees are planted in open habitats that support breeding waders, numbers usually decline pretty quickly. Trees not only directly remove once-occupied habitat, they are also thought to attract predators, by providing somewhere to hide. In their paper in Restoration Ecology, Mark Hancock and colleagues investigate the distribution of thousands of scats of mammalian predators, in order to understand predator activity in landscapes associated with open bogs and forest edge. They were particularly interested in seeing how long it takes for predators to move out of an area when trees are removed and the land once more reverts to blanket bog.

This study took place alongside a project to repair damage to the vast Flow Country blanket bog (northern Scotland), that occurred in the 1980s, when non-native conifer trees were planted in areas of deep peat that had been drained and deep-ploughed. Such forestry practises would nowadays be prohibited.

More trees

The spread of trees can occur naturally, as the northern treeline moves further north or as trees grow higher in mountain regions, or it can be imposed or accelerated when trees are planted in previously open environments. Warmer temperatures create more opportunities for afforestation and politicians seem to be responding to rising CO2 levels by opting for what seems like an easy win – ‘let’s plant more trees’. In the right places, using appropriate native species, woodland can help to capture carbon**, support woodland wildlife and provide multiple other benefits to society. However, if afforestation focuses on open wet landscapes it can potentially threaten ground-nesting wader species such as Dunlin and Curlew.

** link to The value of habitats of conservation importance to climate change mitigation in the UK by Rob Field and colleagues in Biological Conservation.

As Mark Hancock and colleagues indicate in the abstract of their paper, afforestation of formerly open landscapes can potentially influence mammalian predator communities, with impacts on prey species like ground-nesting birds. In Scotland’s Flow Country, a globally important peatland containing many forestry plantations, earlier studies found reduced densities of breeding waders on open bogs where forestry plantations were present within 700 m. See Hancock et al. 2009 and Wilson et al. 2014. A previous WaderTales blog discussed whether apparent avoidance is due to actual or perceived predation risk (See Mastering Lapwing conservation) but whichever it is, adding new woodland to open wetland habitats has the potential to affect sensitive breeding waders.

Fox scat

There have been many studies looking at the effects of trees on breeding waders but the key differences in this case were that researchers monitored how mammal distributions changed as woodland was removed, in an effort to restore biodiversity and valuable blanket-bog habitats. Spoiler alert: it takes several years to reduce predator numbers!

By counting scats of species as diverse as fox and hedgehog the team were able to address three questions:

  • Did scat distributions vary between open bog, forestry plantations, and former plantations being restored as bog (‘restoration’ habitats)?
  • How fast did scat numbers change in restoration habitats?
  • Were scat numbers different in bogs with differing amounts of nearby forestry?

Counting the poo

Forestry transect

The analyses in this paper are based upon surveying 819 km of track verges, which yielded a total of 2806 scat groups (groups of scats that could have come from one animal) from a variety of predators. I smile when days and days of painstaking fieldwork are summarised in a sentence. “We measured summer scat density and size over 14 years, in 26 transects 0.6-4.5 km in length, collecting data during 93, 96 and 79 transect-years in bog, forestry and restoration habitats respectively”. There is no mention of midges either!

The Flow Country is host to a range of predatory mammals. Hedgehog, Wildcat, Red Fox, Badger, Pine Marten, Stoat and Weasel are native species, while introduced species like Feral Ferret and American Mink may be threatening the area. A 10 mm diameter scat could have been produced by one of six or more species – and increasingly it has been shown that genetic methods, which were outside the budget of this study, are needed to properly identify species from a scat. As all of these species prey on the eggs and/or chicks of breeding waders, the study treated them as a ‘guild’ of animals having similar potential effects.

In April each year, fieldworkers – many of them volunteers based at RSPB’s Forsinard Flows reserve – walked along each of the transects, removing all of the scats from the tracks and track-edges. In July, scats and scat groups that had been deposited on the tracks during the breeding season were counted, measured and their positions recorded using GPS (see paper for details).

Nine transects were in open bog habitat, that remained broadly unchanged throughout the study, 8 were in forestry plantations, 8 were in forestry plantations that were cleared and then restored during the study and 1 site was already a restored plot. For ‘restoration’ transects, the number of years since felling was used as a measure of the length of time under restoration management. In these restoration areas, the brash that was left after felling gradually rotted away or became buried by recovering bog vegetation as re-wetting management (e.g. drain blocking) took effect.

Where’s the poo?

Transect through bog

Predator activity in different habitats and over time. For bog and restoration habitats, scat group density was relatively low throughout the study, averaging around 1 to 2 scat groups per km. In forestry transects, scat group densities started at similar values, but rose approximately eight-fold over the study period, as the forests matured. In the final year of the study, scat group densities in forestry averaged around eight groups per km – approximately twice the figures in restoration and six times the figure in bog habitats. There is a suggestion that more mature forests may have suited Pine Martens, in particular: this species was recorded in the heart of the Flow Country for the first time during the study period.

Trees removed – restoration transect

Predator activity once trees are removed.  Scat group density differed significantly between restoration areas of different age classes. In recently-felled sites (1-5 years), densities were about 2.4 groups per km, rising to 4.0 in the middle period (6-10) and falling to 1.3 later (11-14 years). The authors suggest that tree removal may lead to a flush of nutrients, grasses and then small mammals, thereby explaining the increase in scat densities during the middle stage (6-10 years). The paper demonstrates that it takes several years for mammal densities to fall back to ‘natural’ levels, after tree removal.

Pine Martens have moved into the area

Predator activity close to forests. Scat density on open bog transects was significantly affected by the presence of at least 10% forestry cover within 700 m. There was an estimated 2.9 times (95% confidence limits 1.4 to 6.0) higher scat density at bog transects which contained over 10% cover of forestry within 700 m, compared to bog transects with less forestry nearby. Scottish studies of breeding waders have shown that species such as Golden Plover, Dunlin and Curlew avoid areas close to forestry and the paper includes references to several other similar studies elsewhere.

The Conservation picture

As pointed out by Hancock et al in their Discussion, scat densities in forestry reached much higher values than those of open bogs, especially as the plantations matured, implying that afforestation had strongly altered patterns of mammalian predator occurrence in this formerly open landscape. It took ten years of restoration management to drive down scat densities to levels similar to those of open bogs but, as the authors note, peatland restoration is a rapidly developing field and newer techniques may allow faster restoration, with both biodiversity and soil carbon benefits.

These findings have implications way beyond the scope of this study, three examples of which are included below:

Commercial forestry is seen by some as a way of capturing carbon and can provide opportunities to restore our woodlands, especially our native woodlands and their associated biodiversity. However, given the vulnerability of ground-nesting birds to predation, and the potential for afforestation to markedly affect predator communities, care needs to be exercised when considering afforestation of open landscapes.

Warmer climates offer opportunities to add forestry to the mix of land use options in areas in which the growing season used to be considered too short. For instance, there is significant development pressure in Iceland to plant large areas of non-native commercial forestry. Given that the country holds half or more of Europe’s breeding Whimbrel, Dunlin and Golden Plover this is a contentious issue. This AEWA report is important: Possible impact of Icelandic forestry policy on migratory waterbirds.

In Ireland, it has been suggested that a patchy distribution of relatively new forestry plantations may be one of the factors contributing to the drastic decline of Curlew numbers. (Ireland’s Curlew crisis describes a 96% decline in just 30 years). It has been proposed that some of these patches should be removed. The Hancock et al paper shows how long it might take to make a difference – ten years may simply be too long for Ireland’s breeding Curlew.

Read more

The paper that forms the basis of this blog is:

Guild-level responses by mammalian predators to afforestation and subsequent restoration in a formerly treeless peatland landscape by Mark H. Hancock, Daniela Klein and Neil R. Cowie. Published in Restoration Ecology. https://onlinelibrary.wiley.com/doi/abs/10.1111/rec.13167


GFA in Iceland

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

@grahamfappleton

Plovers from the north

Despite its global distribution, the Grey Plover (or Black-bellied Plover in the Americas) does not get the attention it deserves, according to Andrew Darby, author of Flight Lines, a book about shorebird migration and Grey Plovers in particular.

Who would want to study a shorebird that is the first species to sneak away from its tundra nest when danger threatens, and that is hard to catch outside the breeding season? Fortunately, satellite technology means that a lot can be discovered by following just a small number of birds and this blog will focus on two individuals, setting their travels within a broader flyway context.

Flight Lines

Grey Plovers CYA and CYB are the stars of Flight Lines, a book by Andrew Darby which takes us ‘across the globe on a journey with the astonishing ultramarathon birds’. They were caught together in Adelaide’s Gulf St Vincent by members of Victoria Wader Study Group on 14 November, 2015. Here, they were carefully fitted with tags that were originally to be deployed on Bar-tailed Godwits. So starts a story that takes us from the south coast of Australia to islands off the north coast of eastern Siberia, via the Yellow Sea.

Andrew has not simply written a bird book; Flight Lines tells the sort of tale that I remember from school days, of how Cook and Magellan travelled the globe or Livingstone and Stanley ‘discovered’ Africa. Grey Plovers have been flying to the Arctic for millennia – from Europe, Africa, Asia, Australasia, the USA and South America. CYA and CYB are doing what their ancestors have always done. As we follow their journeys, Andrew tells us about the habitats these birds need, shares stories about the lives of local people who await their arrival, reveals the way that shoreline ‘development’ is impacting upon their survival and tells us about some of the ornithologists who are  encouraging governments and local communities to save space for the birds with black wing-pits (see picture below).

Territoriality

Grey Plovers travel vast distances across the globe but once they have arrived at their final destinations they are highly territorial – and not just in the breeding season. When David Townshend studied marked individual Grey Plovers feeding on the Tees, in north-east England, back in the late 1970s, he discovered that they fed in the same places for the four-month period of the winter, defending their patches against interlopers; what’s more, they returned to these territories in subsequent years. It’s like running a marathon and then not leaving your back yard until it’s time to take off again, months later.

As Andrew Darby reminds us, Grey Plover can re-visit the same territories for decades; something to remember when considering what happens when a coastal development steals the ‘homes’ of all of the Grey Plovers in a bay. How does a twenty-year old bird find a new home? There’s a WaderTales blog about longevity records for waders/shorebirds.

Territoriality is not just a British thing. In Flight Lines we learn that the same is true for American Black-bellied Plovers wintering in San Diego and Grey Plovers in South Africa’s Eastern Cape. Here, tracking has shown that the patterns that David Townshend witnessed by day are maintained during the night. Those big eyes can make the most of low light-levels. A hungry individual stands still and waits for prey to move, gives up after a while and tries another likely patch within its territory. Plovers are not like Knot; they don’t have a sensitive tip to the bill that can detect hidden prey, their hard-tipped bills grab items from the surface of the mud or sand, guided by those big, black eyes.

Global distribution

According to BirdLife International, the global population of Grey Plover is only about half a million birds, 80,000 of which use the East Asian-Australasian Flyway. This system of aerial ‘motorways’ links countries as diverse as New Zealand and Thailand with breeding areas in the East Russian Arctic and Alaska.

There is a temptation to sit at home and think of migration as something that happens in a line that runs north to south and back again. Fifty years ago there was an assumption that Black-bellied Plovers would migrate north and south within the Americas, that Grey Plovers in western Europe and Africa would be linked to western Siberia, that Australian birds bred in eastern Siberia, and that Grey Plovers in southern Africa, the Arabian peninsula, India etc  would be birds that had flown from ‘the middle bit’ – between western and eastern Siberia.

Studies of other shorebirds have shown more cross-overs than might have been expected, breaking up the neat south-north pattern. Chukotka, for instance, indicated by the red star on the BirdLife map, is a summer home for Ringed Plover from Egypt (Well-travelled Ringed Plovers), Spoon-billed Sandpipers from Bangladesh, Knot from Australia and Buff-breasted Sandpipers from South America.

Shorebird mixing happens on the other side of the Bering Sea too. Shorebirds that fly to Alaska from South America in spring are joined by Bar-tailed Godwit that fly north from New Zealand, via the East Asian coast. These baueri race Bar-tailed Godwits are famous migrants – they fly non-stop all the way to New Zealand come fall/autumn. See paper by Phil Battley et al.

So, what about Australian Grey Plovers? Do they meet up with American Black-bellied Plovers?

Linking wintering and breeding areas

As Andrew Darby tells us in Flight Lines, measurements of Grey Plovers in Australia and in Russian breeding areas suggested that wader experts Clive Minton and Pavel Tomkovich were handling the same birds in Victoria and on Wrangel island, north of the Russian mainland. In 2007, Pavel banded some Grey Plovers, the hope being that one of them might be seen in Australia. The only one of these Grey Plovers ever to be reported was seen in the Chinese part of the Yellow Sea – six years later.

The Grey Plover colour-ringed by Pavel was spotted by David Melville, who has done a great deal to fill gaps in knowledge about the vast flocks of waders that use the Yellow Sea, including significant numbers of passage Grey Plover. One of the wonderful features of Flight Lines is the way that it turns names into characters. I had heard of many of the people who Andrew met or spoke to, during research for the book, but I appreciate their roles much better now. There is fantastic work taking place in countries throughout the Flyway, ably coordinated through the East Asian-Australasian Flyway Partnership.

Given that colour-ringed Grey Plovers were not providing the data that could link breeding and wintering grounds, it was time to try something new. On 14 November, 2015, CYA and CYB were fitted with satellite transmitters and in March they flew north. In the same way that we read that Captain Cook ‘discovered’ Australia, without telling the story of the challenges his crew faced on the way, I am just going to present the map of the northward journeys of the two birds and leave you to read Flight Lines, the log-book of their journeys.

The map shows the positions on 7 June 2016, whe CYA and CYB had only just arrived on Wrangel Island. The journey north is described by Tony Flaherty in Victoria Wader Study Group Bulletin number 39.

“The two satellite transmitters, put on to Grey Plover in South Australia by Maureen Christie’s team in November, 2015, have performed brilliantly, with both birds successfully migrating northwards, including a long stop-over in the Yellow Sea, and eventually going on to breed on Wrangel Island off the north coast of Chukotka, eastern Siberia. This is the first evidence of any bird from Australia visiting this remote Arctic Island. At the time of writing this, both are now on their way back from the Arctic, with one having made a surprising major detour via the New Siberian Islands.”

There is a complementary article about the journey south in the next issue of the VWSG Bulletin, also by Tony Flaherty.

Map data courtesy of Victorian Wader Study Group & Friends of Shorebirds SE. The project was made possible by support from the Australian Government and the Adelaide and Mt Lofty Ranges Natural Resources Management Board.

A conservation agenda

One of the major drivers of bird ringers/banders is a thirst for knowledge – and there is nothing wrong with that spirit of enquiry. For the East Asian-Australasian Flyway there is a deeper imperative; conservation of birds using habitats that are under immediate threat from human exploitation and climate change. A previous WaderTales blog – Wader declines in the shrinking Yellow Sea – focuses on a paper that highlighted the desperate need to understand and conserve shorebird populations. One species that hardly gets a mention in that paper is the Grey Plover. It’s not that there is no threat to Grey Plovers, it’s just that there were insufficient data. It’s not easy to study these territorial plovers, which are thinly spread throughout the non-breeding range and difficult to catch.             

About Flight Lines

The WaderTales blog series started out as a planned book about Black-tailed Godwits but I found that I did not have the stamina to weave together science tales into an interesting tapestry. Andrew Darby is a master of the writing craft. Although he focuses upon waders, and the Grey Plover lead characters, he also tells us about the pioneer ornithologists who have explored the East Asian-Australasian Flyway, in search of shorebirds that spend Christmas and New Year in Australia and New Zealand. Flight Lines is published by Allen & Unwin. ISBN 978 1 76029 655 1

Migration research about other Grey Plover populations

Papers about Grey Plover and Black-bellied Plover are thin on the ground but new projects on the East Atlantic Flyway and in the Americas are starting to fill in some of the gaps in our knowledge.

The Wash Wader Ringing Group has ringed/ banded over 6500 individual Grey Plovers since the Group was founded in 1958 (Sixty years of Wash waders). Their work was written up in 1976 by Nick Branson and Clive Minton (Moult, measurements and migrations of the Grey Plover). The map alongside shows movements of birds to and from the Wash.

Recent research by Klaus-Michael Exo and colleagues has used satellite tracking to understand better the movements of Grey Plover breeding in the Taimyr and Yamal regions of Siberia. In their paper, they identify important staging sites as well as wintering areas between Ireland and Guinea Bissau. Tagged birds stopped off for long periods during migration, especially in late summer and autumn. See Migration routes and strategies of Grey Plovers on the East Atlantic Flyway as revealed by satellite tracking.

The Tidal Wings project focuses on Grey Plovers that winter in the Bijagos archipelago of Guinea Bissau. You can keep up to date on their discoveries on their website (https://birdecology.wixsite.com/tidalwings) and on Twitter. The map above shows three migrations of the same individual.

In North and South America, the Black-bellied Plover is also receiving increased attention. There is a large collaborative project to reveal their migratory connectivity, with over 70 tags deployed to track birds from Alaskan and Canadian breeding grounds, and from Texas and Louisiana wintering grounds. Work is being conducted by the Smithsonian’s Migratory Connectivity Project, USGS Alaska Science Center, Environment Canada, Texas A&M University, University of Missouri, Brighman Young University-Hawaii, and Coastal Bend Bays and Estuaries Program. The map alongside was provided by Autumn-Lynn Harrison of the Smithsonian Migratory Bird Center and shows example migration routes from one breeding population in Nome, Alaska. 

Colour-ring studies. Satellite tags are a key part of modern wader and shorebird studies, providing immediate insights from just a small number of birds, but simple bits of plastic can play a role too, especially in Western Europe, where lots of birdwatchers visit coastal sites. Colour-ring studies in East Anglia and northwest England are revealing more about how Grey Plovers use a suite of different estuaries during the course of the non-breeding seasons and will ultimately monitor annual survival rates. It will be interesting to learn whether individual birds hold territories in each of the estuaries that they visit, to moult, spend the winter and prepare for spring migration. The importance of allocating individual leg-flags to ringed birds is discussed in Bar-tailed Godwit: migration & survival.

I look forward to seeing more papers about the Grey and Black-bellied Plover, the shorebird that breeds at the top of the world.


GFA in Iceland

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

@grahamfappleton

A Rhapsody of Whimbrel

Around the globe, the seven-note whistle of the Whimbrel is a spring theme tune for shorebird migration. Where are flocks going to, as they gain height and head north in March, April and May, and why have birds chosen that particular moment to depart?

In a paper in Frontiers in Ecology & Evolution, Camilo Carneiro, Tómas Gunnarsson and José Alves analyse individual migration tracks of birds flying from West Africa to Iceland, including journeys made in successive springs by birds that have been part of the same study for several years. Can these birds help to explain how Whimbrel use time and weather cues in their travel ‘planning’ and might their plans change during the course of their lives?

Look up to the skies and see

Almost all of the Whimbrel that nest in Iceland migrate to West Africa after the breeding season, with just a tiny number wintering in Europe.

Life has just begun

The Whimbrel’s story starts in Southern Iceland. It would be great to tag chicks when they hatch, in order to learn what happens to juveniles in their first autumn, as they head south without parental guidance. For the moment, however, Camilo Carneiro, José Alves and Tómas Gunnarsson are focusing on parent birds which they have been catching on their nests since 2012.

The research summarised in the paper at the heart of this blog uses data from 66 retrieved geolocators that have been carried by a total of 39 individuals.  Light data, temperature readings, conductivity and the timing of contacts with water all help to determine the start and end points of individual flights.

Any way the wind blows?

As the authors write in the summary of the paper, “Weather conditions are important during migration, particularly wind and temperature, and can play a crucial role in the timing of events during the annual cycle of migratory birds.” Camilo and his colleagues have investigated how wind conditions, temperature and spring departure date may drive individuals to pursue either a ‘stop-over’ or ‘direct flight’ strategy in the spring. They suggest that one or two of the following scenarios might be envisaged:

Competition on the breeding grounds can be quite vigorous
  • Whimbrels may make migratory decisions prior to departure, given local weather conditions. If migratory behaviour is defined prior to departure then that would suggest that departure time from West Africa may not be associated with the wind conditions that can assist individuals on the first stage of their journeys.
  • Whimbrels may adjust migratory behaviour during flight, depending on conditions experienced en route. As birds fly north, from 37°N (level with the Mediterranean) to 50°N (SW tip of England), they can make decisions to stop off, rather than continue straight to Iceland. Potentially, they could assess the amount of support they have been receiving from favourable winds and assess the positive effect on fuel reserves. Temperature could also act a cue to weather conditions in Iceland.

Little high, little low

Wader biologists and birdwatchers will have seen flocks of waders preparing for departure from breeding, stop-over and wintering locations.  Birds become restless and groups of birds start to circle and rise into the sky.  The first, departing flock may be joined by others, taking off in small groups to catch up with birds that seem to have a plan. At the same time, birds can also be seen dropping out of the flock to wait for another day.

Once formed, a migratory flock will be made up of individuals that may be heading for points that are hundreds or (for some species) even thousands of kilometres apart but will fly together for this next leg of the journey.

Tómas Gunnarsson has seen Whimbrel circling and gaining height at departure from the south coast of Iceland in autumn, suggesting that they may assess wind conditions at different altitudes before making a final decision and setting their course south. It seems plausible that the same sort of thing might happen during spring migration from West Africa. At some stage, with a large number of tracked birds, perhaps it will be possible to study if waders sample wind speed and direction prior to departure and whether decisions made at this point affect the amount of support they receive from wind conditions when on migration. There’s a great paper about how wind affects the migration of much larger Honey Buzzards by Wouter Vansteelant.

Once in the air, birds in a migrating flock can be impeded by headwinds, assisted by tailwinds and pushed laterally by crosswinds. As has been shown when tracking trans-Pacific journeys of Bar-tailed Godwits, storms and pressure systems can provide a sling-shot effect to accelerate progress, cause birds to temporarily abort their journeys or even back-track a thousand kilometres, in order to refuel for another migration attempt.

Nothing really matters

Camilo and his colleagues compared 9 direct flights with 48 that included stops in Portugal, France, Ireland and north-west Britain. Birds that departed later tended to undertake direct flights. Interestingly, they found little evidence that conditions were linked to an individual’s migration option:

  • For individuals undertaking either direct flights or stopovers, the wind conditions at departure did not differ from winds during the previous seven days, suggesting little or no selection for wind conditions to initiate the flight.
  • Individuals on direct flights encountered similar winds as they passed through the region 37°N to 50°N (Mediterranean to SW tip of England) as those on stop-over journeys.

Too late, my time has come?

For late-departing birds that fly straight to Iceland, there is the potential to catch up with (and even overtake) birds that left earlier and subsequently stopped in countries such as Ireland. In such circumstances, one could imagine that birds still in West Africa in late spring may ‘opt’ for a direct flight. However, the wind patterns over a period of seven days prior to departure were no different to the ones at the start of a non-stop flight. There did not seem to be any weather-related reason for these birds delaying departure as long as they did.

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Camilo Carneiro is also investigating the breeding success associated with different arrival times and migration patterns

For birds that do stop-off en route in Britain and Ireland, which are relatively close to the breeding sites in Iceland, there are potential benefits, as discussed in more detail in the paper:

  • Individuals might be able to assess (remotely) the weather conditions at their breeding sites if there are links between weather patterns in Iceland and those in Ireland and western Britain. If this is the case, then they can adjust the start of the final Atlantic crossing so as to arrive in Iceland when conditions are likely to be favourable.
  • Whimbrels can feed up in Britain & Ireland, potentially arriving in Iceland in better condition than birds that have flown directly from West Africa.

Carry on, carry on

The fascinating thing about being able to track individuals is that we are starting to understand the conditions that may lead to the migration patterns we see at the population level. In other WaderTales blogs, some of the key processes and patterns have already been discussed:

Given this body of knowledge, suggesting little flexibility once an individual’s phenology is fixed, one might expect that an individual Whimbrel, travelling from West Africa to Iceland, would adopt the same migration pattern in subsequent years. Tagged Whimbrels, for which there were repeat migration tracks, mostly ‘did the same’ but not always.

Any way the wind blows, doesn’t really matter

The key finding of Camilo Carneiro and his colleagues is that weather conditions are not the main driver of different spring migratory timings in Icelandic whimbrels. As suggested in Whimbrel: time to leave (and the paper Why are Whimbrel not advancing their arrival dates into Iceland?) departure from West Africa is the most firmly scheduled point in a Whimbrel’s annual cycle. However, three birds provide an opportunity to build a modified hypothesis.

In the course of this study of Icelandic Whimbrel, thirteen birds have provided multiple years of data and there have been three cases in which birds have switched migratory behaviour, seemingly contradicting the ‘birds always do the same thing’ theory. In each case, individuals changed from ‘direct-flight’ to ‘stop-over’ and, having changed, they then repeated the ‘stop-over’ option. The fact that all three individuals made the same change hints towards individual refinement of behaviour. Since there appears to be no clear advantage to direct migration, perhaps individuals are moving to a two-stage migration when they discover that this is a possibility?

Is this just fantasy?

This is where the paper stops but it will be fascinating if the research can continue:

  • Are changes always going to be in the same direction – from ‘direct-flight’ to ‘stop-over’?
  • Most juveniles are thought to fly directly to West Africa. By tracking young birds, caught in Iceland prior to departure, perhaps it will be possible to work out the proportion of first journeys that are direct?
  • Young birds that fly south across the Atlantic will not have learnt that there is any land between Iceland and West Africa. Do they retrace their journeys when they fly north again, eighteen months later?
  • What proportion of these birds that start on the ‘direct-flight’ strategy later switch to ‘stop-over’?
  • If some juveniles stop off in western Europe, on their first journeys south, perhaps these birds also stop off on their first journeys north? That might mean that they never used the ‘direct-flight’ option.
  • And how do flocks work? Will it ever be possible to deploy enough trackers to see whether ‘direct-flight’ individuals learn that there’s an alternative option by travelling in flocks with birds that use the ‘stop-over’ strategy.

It’s all fascinating stuff about the Queen of waders!

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Anyone can see

The paper featured in this blog is: Linking weather and phenology to stopover dynamics of a long-distance migrant by Camilo Carneiro, Tómas G. Gunnarsson & José A. Alves, published in Frontiers in Ecology & Evolution.


GFA in Iceland

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

@grahamfappleton

Scotland’s Dotterel: still hanging on

blogpic brooding

Dotterel brooding chicks

Within the UK, the Dotterel now only breeds on plateaux in the highest Scottish mountains, restricted by habitat that is more commonly found in the arctic or arctic-alpine regions. 

As soon as climate change became apparent, the Dotterel turned into a focal species for ornithologists who were interested in how species would be affected by climate heating. Their fate seemed to be sealed; put simply, there is nowhere colder in Britain to which to retreat when faced with changing habitats and/or breeding conditions.

A 2020 paper by Steven Ewing, Alistair Baxter and colleagues explores the potential ways that changing environmental conditions may be driving the Dotterel’s decline.

Life history

Scottish Dotterels don’t actually spend much time in Scotland, with most birds arriving in early May and leaving within three months. The large part of the year is spent in North Africa, and the plains to the northwest of the Atlas Mountains in Morocco seem to be a particularly important wintering grounds for Scottish birds. Migration north and south appears to be direct, with few European reports of ringed birds in spring and autumn. There is some evidence that Dotterel move further south within North Africa as winter progresses (Whitfield et al 1996), perhaps responding to rainfall patterns.

blogpic map

In May, the numbers of males and females on Scottish breeding sites are roughly equal but many females leave their males sitting on a first clutch of eggs and then depart, leading to an observed drop in sex ratios to about 10:1. Females ringed in Scotland have been spotted breeding with Norwegian males later in the same season and this onward movement to areas with later snow-melt may well be a normal pattern. Indeed, many Dotterels seen on passage in May, often on traditionally used fields or mountain tops south of the Scottish Highlands, may loop north, passing through Highland nesting haunts and then heading northeast into Scandinavia.

A species in decline

blogpic Alistair

Alistair Baxter points to a Dotterel nest that’s right next to a path following the line of a ridge

Dotterels in Britain are at the south-western limit of the species’ global range. They breed almost exclusively in arctic-alpine habitats above 750 m, particularly on Racomitrium moss-heaths that are so characteristic of the flatter topped mountains. These habitats are of high conservation concern, with a tapestry of nationally-rare alpine and arctic plant species.

Scottish Dotterel have been well-studied for over eighty years, a process that was started by Desmond Nethersole-Thompson in the 1940s (detailed in his classic monograph The Dotterel, 1973) and has involved the authors of the Global Change Biology paper since 1987. Some of the areas featured in this paper were studied by Nethersole-Thompson.

An earlier WaderTales blog (Dotterel numbers have fallen by 57%) suggested a number of possible reasons for declines – habitat changes, increased predation and increased disturbance in the Scottish Highlands, compounded by issues affecting the wintering population in North Africa. In the 2020 paper, Ewing et al look in more detail at the potential roles of these changes

Climate and habitat change in Scotland’s mountains

Mountains in Britain are subject to a range of environmental drivers of change that may potentially influence Dotterels, but the logistical challenges presented by working in these environments means that there is rarely good data documenting these changes. This study focuses on snow cover and nitrogen deposition.

blogpic change

The amount of snow-cover is important for cold-adapted species of plants and animals; it insulates the ground in winter and slows up warming in spring, thereby creating a relatively stable environment.  Potential consequences of changes in winter snow-lie for alpine birds might include:

  • A longer growing season for plants, with taller vegetation that reduces the suitability of these areas for species that favour shorter swards.
  • Fewer snow patches, around which Dotterel feed, perhaps also leading to a reduction in peak insect abundance that may not match feeding requirements of chicks.

blogpic nestLots of research carried out in the UK shows that nitrogen deposition is an important driver of upland vegetation change.  Higher deposition of nitrogen tends to result in a reduction of alpine specialist plants, including species of mosses that form key breeding habitats for Dotterel.

The earlier WaderTales blog (Dotterel numbers have fallen by 57%) suggested other possible reasons for Dotterel declines on the breeding grounds, including increased predation and increased disturbance in the Scottish Highlands. While these potential drivers of change could not be tested, due to a lack of data, they are considered in the paper’s Discussion.

Study system

The data that lie at the heart of the Global Change Biology paper have been collected over three decades. Two different but complementary data sources were used in the study.  Firstly, Dotterel were counted at between 128 and 198 alpine sites in the UK during three national surveys in 1987-88, 1999 and 2011.  These censuses focused upon suitable breeding habitats, especially Racomitrium heath, with the latter two surveys successfully covering more than 50% of identified breeding areas.  Secondly, between 1987 and 1999, a smaller cohort of alpine sites were surveyed with far greater frequency (between 40-60 times) as part of SNH’s Montane Ecology Project, where the aim was to study the Dotterel’s breeding ecology in far more detail. The 2020 paper contains detailed information about site use and the parameters that were measured/assessed (elevation, slope, area, snow cover, nitrogen deposition, summer temperature etc.)

blogpic surveyEach site visit involved a lot of climbing, so many of the sites were visited only once per season, with more frequent visits to just 15% of the sites. Having accompanied Phil Whitfield (one of the authors) up one mountain, on one day, I have huge respect for the effort that each data-point represents.  Once up on the tops, observers covered the study areas thoroughly, passing within 100 m of every point and scanning frequently. This has been shown to provide a good count of breeding males.

The authors used their data to investigate whether key potential drivers of environmental change in Scottish mountains (snow-lie, elevated summer temperatures and nitrogen deposition) may have contributed to the population decline of Dotterel.  They also consider the role of rainfall on the species’ wintering grounds in North Africa. The key questions they address are:

  1. Is there evidence of an uphill shift in the elevation of the Dotterel’s breeding range during the study period (1987-2014)?
  2. Are changes in the density or site occupancy of breeding male Dotterels associated with the size, connectedness or topographical aspect of alpine sites?
  3. Does spatial variation in atmospheric nitrogen deposition account for variation in density or occupancy of breeding males at alpine sites?
  4. Are patterns of snow cover or late summer temperatures associated with density or occupancy of male Dotterels at alpine breeding sites?
  5. Do densities of breeding male Dotterels on alpine sites vary with conditions on the North African wintering grounds, as reflected by winter rainfall?

blogpic gloaming

What has changed?

The results are presented in two ways. Data from the period of intensive studies, between 1987 and 1999, are used to try to understand factors influencing annual changes in the number of nesting males. Examination of changes between 1987-90 and 2011-14 gave some indication of factors affecting longer-term trends – something that is important to understand when Dotterel can live for at least ten years.

Densities of breeding male Dotterel in mountainous regions of Scotland declined between 1987 and 1999 and, over the longer-term, site occupancy fell from 80% in 1987 to only 36% in 2014. Densities of breeding males declined disproportionately from lower-lying sites, which resulted in the Dotterel’s breeding range retreating uphill at a rate of 25 m per decade.

Geographically isolated sites appear more likely to lose breeding Dotterel. This makes sense; playback studies in Russia have shown that passing flocks of Dotterel respond to calls, suggesting that birds will be attracted to already-occupied locations.

Settlement patterns were linked to snow-cover.  Generally, Dotterels appear to prefer to settle on higher sites, but late-lying snow at higher elevations appears to deprive them of suitable breeding habitat.  Rather than delay nesting, it seems that these birds then choose to move to lower snow-free sites to breed. Long-term changes in snow cover are poorly documented in high-elevation habitats in Scotland, so it is difficult to know whether the substantial declines observed for Dotterel in recent decades reflect systematic changes in snow-lie.

blogpic snow patch

Nitrogen deposition was shown to be negatively associated with densities of males nesting at lower and intermediate elevations.  The primary impact of nitrogen deposition on Dotterel is likely to be via effects on the species’ favoured Racomitrium moss-heaths, with greater nitrogen levels increasing the rate of moss decomposition and favouring accelerated grass growth.  This presumably results in these habitats becoming increasingly unsuitable for breeding Dotterel.

blogpic chick

Will this chick makes it to Morocco? If it does, how will the conditions it experiences in the non-breeding season affect its probability of return to Scotland?

High rainfall in North Africa seems to lead to higher densities of breeding male Dotterel two springs later, suggesting that wintering ground conditions can potentially influence population dynamics of this alpine-breeding bird.  Similar positive impacts of North African rainfall have also been seen in Ring Ouzels that breed in the UK (Beale et al. 2006).

Dotterel inhabit open farmland and sub-desert steppes in North Africa, where seasonal rainfall brings a flush of vegetation growth and insect abundance. Higher winter rainfall may increase prey availability and Dotterel survival rates but that would be reflected in the arrival numbers in the next spring. The lag of an extra year suggests that low rainfall levels may mostly affect young birds, perhaps delaying recruitment of some Dotterels until their second breeding season.

Conclusions

blogpic juvvyPopulation declines and site abandonment by Dotterel in Scotland during the last three decades have largely occurred at lower elevations, fitting with the traditional idea of climate change limiting the available climate space for alpine breeding species. However, this study found relatively limited evidence that the decline in the breeding population is being driven by climatic factors on the breeding grounds.

Snow cover does seem to influence year-to-year variation in the species’ elevational distribution in Scotland, potentially because a smaller population may now be increasingly settling on higher sites that perhaps were previously unavailable, due to extensive snow cover.  There was also some evidence that greater nitrogen deposition reduced breeding densities of Dotterel at low to intermediate elevations, perhaps by decreasing the suitability of Racomitrium moss heath breeding habitats.  It is also possible that there may have been a redistribution of birds, with newer generations moving further north, to more suitable sites in Norway. (There is a WaderTales blog about this sort of Generational Change mechanism in waders, focusing on Black-tailed Godwit).

Given that Dotterels spend so little time in Scotland, a big gap in our understanding is what is happening in Morocco, where adult Scottish Dotterel spend three-quarters of the year and where young birds may also spend their first summer. How are factors such as rainfall and land-use (particularly farming methods) affecting Dotterels? Might changes in these areas affect other species of migrant that leave northern Europe at the end of the breeding season? Perhaps conservation scientists need to head south for the winter to find out?

Read more in the paper

Clinging on to alpine life: investigating factors driving the uphill range contraction and population decline of a mountain breeding bird. Steven R. Ewing, Alistair Baxter, Jeremy D. Wilson, Daniel B. Hayhow, James Gordon, Des B. A. Thompson, D. Philip Whitfield & René Van der Wal. Global Change Biology.

blogpic dewy


GFA in IcelandWaderTales blogs are written by Graham Appleton, 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.

@GrahamFAppleton