New Bar-tailed Godwit Subspecies

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

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

Limosa lapponica yamalensis

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

How many subspecies?

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

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

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

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

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

What’s different?

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

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

Tracking through space and time

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

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

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

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

Body size and shape

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

Genetics

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

A new subspecies

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

Breeding locations of tagged Bar-tailed Godwits

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

Conservation considerations

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

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

Paper

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

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

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

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

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

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


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 flock now departing

“The flock now departing from the tideline is bound for Beauvais. Curlew can change here for destinations in Germany and Russia”. It’s fascinating to wonder what might be happening when a flock of waders takes to the air, gains height and sets off in a particular migratory direction. With more individuals wearing tracking devices, it was only a matter of time until someone would have data that provides clues as to the association of individuals within flocks – as we see in a 2021 paper in Bird Study by Frédéric Jiguet and colleagues: Joint flight bouts but short-term association in migrating Eurasian Curlews.

Setting off on migration

When we get on a plane to a particular destination, everyone else who is on the same journey has chosen to travel at the same time and we all know where we are going. Each of us has checked that we have what we need for the journey and has a plan of what to do when we land – whether that involves a short shuttle to home or a lay-over before catching another flight.

For waders, planning must be more random? It’s presumably safer and more efficient to be part of a flock but how do you know which flock to join, who organises the schedule and is information shared? We can get some clues from observations of departing migratory flocks. In estuaries, there is often the chatter (which is hard to interpret but tells us that something is about to happen), then the first birds take to the air and start to gain height. A few birds may peel off and return to the tide-line while other birds take off and catch up with the departing flock. As the birds gain height, the direction of travel becomes clearer and more birds may decide to return to the mudflats. There is now a migratory flock of birds that are committed to flying in a particular direction. We have no idea how that direction was chosen, of course, but there is a plausible explanation as to how the flock might have formed.

This is not the last decision that members in a flock might need to make. Tired birds may need to drop out of the flock, to take a break. Perhaps some birds might realise that the direction of travel does not work for them and the flock might break up?

It can be just as chaotic when a flock reaches a destination. Watching Black-tailed Godwits arriving in South Iceland in April is fascinating; a tired flock might come in off the sea, land and start drinking, before either resting or feeding, but this is not always the case. On a clear day with fair winds, the flock may split up, with some birds keen to keep flying and others happy to stop. This reinforces the impression that a flock only maintains its integrity as long as being in a group meets the needs of the individuals it contains.

Tracking Eurasian Curlew

Understanding migration is an important element of Curlew conservation studies in France.

In their Bird Study paper, Frédéric Jiguet and colleagues describe four cases of joint migration by tagged Eurasian Curlews. Their observations were a biproduct of research aimed at a better understanding of the origins and migration patterns of Curlew that spend the winter in France. The species has been a popular target for French hunters, many of whom are keen to resume shooting, as you can read in the WaderTales blog Black-tailed Godwit and Curlew in France. It is estimated that more than 7000 Curlew were shot in France annually prior to 2008, when the first moratorium was put in place.

There is an urgent need to understand links between wintering sites and breeding sites, especially in areas where the species is in rapid decline. How important is France to the Curlew that breed in countries such as Poland and Germany? The current ban on shooting is not perfect (see paper in Forensic Science International: Animals and Environments) but it is better than nothing, given rapid declines in Curlew numbers across Europe.

In winter and spring 2020, the research team deployed 61 GPS tags on Curlews in France and Germany, hoping to learn more about breeding ecology and migratory connectivity. In a separate study, in Poland, four captive-bred juvenile curlews were tagged and released in July 2020. Between them, these tagged birds led to four cases of joint migration bouts. One case concerned two adults leaving their wintering ground for the pre-breeding migration. Two other cases were birds leaving their breeding grounds at the start of migration. The last one was of two juveniles initiating their first flights to the non-breeding grounds.

Spring migration

About 27,500 Curlew spend the winter in France (see French report produced jointly by government and shooting groups), representing about 5% of the European population. Tracking has shown that these birds breed in Belgium, Germany, Sweden, Finland, Austria and Russia (see article published by Bird Guides) but there are reports of ringed birds from many other countries, including the threatened populations in Poland and the UK.

Thousands of Curlew spend most of the year in coastal France – representing 5% of the European population.

Return migration to breeding areas takes place in early April. Frédéric Jiguet reports ‘groups of curlews rising high in the sky at sunset’ from the Moëze-Oléron and Baie de l’Aiguillon Nature Reserves in southwest France.

Back-mounted GPS tag

On 17 April 2020, two individuals wearing tracking devices left their French wintering site at sunset, between 22:37 and 22:40. They became closely associated just ten minutes prior to the start of migration, having typically stood 100 metres apart during the previous hour. They flew together for seven hours before making a stop-over north of Paris, between Creil and Beauvais, in the Thérain Valley.

  • 200185 was on its way again two hours later, flew for six hours, stopped again in the Netherlands and arrived in Norderney, an island of the Wadden Sea in northern Germany, at 18:39 on 19 April.
  • 200187 had a much longer layover in the Thérain Valley, making another evening departure at 20:05 on 18 April. It continued migrating, in stages, for more than a month, crossing the Ural Mountains and reaching the Yamalia municipality, in Asian Russia.

Two birds that had been on the same flight from southwest France ended up in very different locations and at very different times. The German Curlew reached its summer destination five weeks before the Russian bird arrived on territory, the latter having secured places on several different ‘international flights’ as it made its way east and north (see figure below).

Post-breeding migration

After breeding, adult Curlew head towards wintering sites, perhaps stopping to moult en route. Some birds do not travel far; for instance, there are colour-marked birds that winter on the Wash (eastern England) and fly just a few kilometres inland to breed. The Bird Study paper includes reports of two occasions when tagged birds have been spotted migrating together from German and French study areas. Southerly migration of all four birds commenced during the evening of 17 June 2020.

French birds: Two individuals departed simultaneously from Deux-Sèvres (central France) between 19:16 and 19:17 for a non-stop southward flight and arrived together at Ria de Treto estuary, in northern Spain on 18 June at 05:49. The two birds departed separately from this stopover site the same day (18 June).

  • 200201 departed at 18:18, for a non-stop flight to Kenitra (Morocco) where it stopped briefly, before moving a short distance north to Merja Zerga.
  • 200204 departed at 19:46 and flew to the Atlantic coast of Spain, stopping for 2.5 hours on Isla Cristina and then flying to its final destination at Ilha de Tavira, in southern Portugal.

After separation, the two birds travelled at different times but followed quite similar routes and even flew at similar altitudes.

German birds: On 17 June 2020, two individuals departed simultaneously from Dollar Bay, in the Wadden Sea National Park. 201075 began migration between 18:58 and 19:03. After five kilometres, if flew over 201072 at an altitude of about 190m. The latter bird took off and joined 201075. They then flew together for five hours, landing in the Rhine-Meuse-Delta (Netherlands).

201075 departed from the Rhine-Meuse-Delta on 20 June and, after one more stop-over, reached its final destination on the Brittany coast on the evening of the next day.

201072 was also bound for Brittany. It departed on 23 June and flew non-stop for six and a quarter hours.

Migration of juveniles

It will be hard to satellite-tag enough wild juvenile waders to pick up instances of marked individuals migrating in the same flocks. However, head-starting may give some clues as to what might happen when naïve flocks of juvenile waders start their migratory journeys, months after the parents have left them. The full story is told in the paper but a quick summary tells us that two Polish head-started Curlews were released on 1 July, departed together on 5 August and landed in the Baie de l’Aiguillon (France) on 8 August. In between times, they came close to landing in The Netherlands, flew along the English coast from Dover to Poole, flew a long way south and west around the Bay of Biscay and then northeast to the coast of France. They both spent the winter in the Baie de l’Aiguillon but not together.

Although it will be difficult to compare the migratory behaviour of wild-caught and head-started wader chicks using satellite tags, just because of probabilities and costs, researchers are building up datasets using smaller geolocators and GPS tags. Here’s hoping that we will soon know more.

Paper

The nutrient-rich mud of Ile Madame

This paper provides observations of just four instances of joint migration but each story is fascinating. They give us insights as to what might be possible as devices get smaller and when land-based tracking stations collect signals from passing birds. For the moment we can use our imagination to interpret the chattering of pre-migratory flocks of waders, the appearance of a small flock of waders at an inland spot in spring and the noisy arrival of a lone Curlew on an estuary in June.

The paper contains a lot more detail about the methods used to collect and interpret data and a discussion that sets Curlew migration within a much broader conceptual context. Here’s a link:

Joint flight bouts but short-term association in migrating Eurasian curlews.

Frédéric Jiguet, Pierrick Bocher, Helmut Kruckenberg, Steffen Kämpfer, Etienne Debenest, Romain Lorrillière, Pierre Rousseau, Maciej Szajdaand & Heinz Düttmann. Bird Study. DOI/10.1080/00063657.2021.1962805

Wintering Curlew from as far away as Russia and Sweden can be found roosting in these French saltmarshes

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.

Flying high with Great Snipe

As tagging devices get smaller and more sophisticated, they are revealing even more wonders of shorebird migration. We already know that Great Snipe are amazing – flying up to 7,000 km non-stop – but a 2021 paper by Åke Lindström and colleagues describes a striking daily cycle of altitude change during their long migratory journeys.

In their new paper in Current Biology, Åke Lindström and colleagues have used activity and air pressure data from multisensor dataloggers to show that Great Snipes repeatedly changed altitudes around dawn and dusk, between average cruising heights about 2,000 m (above sea level) at night and around 4,000 m during daytime. Most birds regularly flew at 6,000 m and one bird reached 8,700 m, an altitude that is just 150m short of clearing the top of Mount Everest! The same daily cycle was apparent everywhere – independently of climate zone, habitat and the height of the land being overflown. Wherever they are, as morning breaks migrating Great Snipes gain altitude – but why?  

Great Snipe

Great Snipe spend the winter in Africa, between 20 degrees south and 15 degrees north of the equator, heading north in spring to breeding areas in Scandinavia and northern Europe, as far east as 95°E (which is the same longitude as Myanmar).

The first paper to reveal the remarkable migration of Swedish Great Snipe appeared in Biology Letters in 2011, when Raymond Klaassen, Åke Lindström and colleagues revealed the tracks from three birds carrying geolocators. During these journeys, these individuals made long and fast autumn movements, covering between 4300 and 6800 km in two to four days and overflying suitable stopover sites that were used in spring. Ground speeds of 15 to 27 m/s are equivalent to between 54 and 97 km/h (33 to 60 miles per hour).

In 2016, using 19 tracks from four years of captures and recaptures, the same team published a paper in the Journal of Avian Biology. About half of the birds flew directly from the breeding grounds to sub-Saharan Africa, the others making a few shorter flights down through Scandinavia before embarking on a long trans-Sahara flight. Birds took advantage of wet seasonal conditions in this Sahel region for three weeks before moving south to the Congo Basin. Spring migration consists of a rapid movement across the Sahara, only a little shorter than the very long non-stop autumn fights, followed by slower movements through Eastern Europe. Birds arrived back on breeding areas in mid-May.

Great Snipes spend about eight months of the year in sub-Saharan Africa. In a 2017 paper in Wader Study, Edouard Debayle, Åke Lindström and colleagues analysed the moult and fattening patterns of over 3,000 hunted birds, to try to learn more about the phenology of migration. They discovered that:

  • Adult males arrived in Africa from mid-August, having started and suspended the moult of the main flight feathers before arrival.
  • Females on average arrived somewhat later and were about one month behind in the progress of flight feather moult.
  • The adults of both sexes resumed primary and secondary moult immediately upon arrival and typically completed it by the end of November, in males, and the end of December in females. Juvenile Great Snipes arrived later than adults and did not moult their flight feathers in the first autumn/winter.
  • Males apparently departed northwards between late March and late April, and the females about two weeks later. There is information about rates of fat deposition in the paper.
Great Snipe watches on as team members set a mist net

Flying high

Processing the catch

Several factors could influence the flight altitude of migratory birds. For example, how high is the land over which birds fly, what are the best temperatures and humidity conditions for efficient flight, at what height can a bird find the most helpful winds, can a bird use navigation landmarks and how can predation best be avoided?

Recent tracking of migratory birds of a range of species has shown that individuals change flight altitude more commonly and dramatically than previously thought but why? In their paper in Current Biology, Åke Lindström and colleagues reveal information from 25 tracked Great Snipe journeys and discuss the reasons that may lie between the patterns that they see.

Methods

Information about behaviour and flights was collected from multisensor dataloggers, consisting of an accelerometer for activity measurements, a barometric pressure sensor with internal temperature sensor, a light-level sensor, a real-time clock, and memory. The dataloggers weighed 1.4–1.7 g (about 1 % of a bird’s total body mass) and were attached to a plastic ring on the bird’s tibia.

In total, 107 dataloggers were put on Great Snipes between 2015 and 2019. Of these, 36 birds were retrapped one, two or three years later (but four birds had lost their loggers). This is an overall recapture rate of 34%, which is similar to the figure for ringed birds. In total, 25 out of the 32 retrieved loggers had functioned for some time, and 16 carried information on flight altitude for at least one of the long flights.

The methods section provides full details of how geolocator data were interpreted and altitudes were calculated and adjusted. Information on air temperatures at different altitudes and the topological features on flight paths provided a background against which to try to understand migration patterns.

How high?

The new data from a small number of multisensor data-loggers greatly enriched the migration story of Swedish Great Snipe, as revealed byÅke Lindström and colleagues. The key results in the Current Biology paper are:

Breeding habitat in Sweden

Flight duration: There were three long flights, two legs on the way south and one on the way north. As noted earlier, northerly migration slowed once birds landed in Europe.

  • On average, male Great Snipe left Sweden on 24th August and flew across Europe and the Sahara for 73.4 hours, before landing in the Sahel.
  • The mean departure date from the Sahel was 24th September. An average of 23.2 hours later a bird would land in the Congo basin.
  • Northerly flights commenced on 18th April, lasting an average of 82.4 hours and concluding in Europe.

Cyclic flight altitudes: There was an overall strong and consistent daily cycle in the altitudes used by the Great Snipes, in all three long flights. After a night at moderate to high altitudes the birds ascended to very high altitudes in early morning, stayed at these levels during the day, and descended again in late afternoon. They then repeated this cycle for one or two more days.

  • The mean individual daytime flight altitude in the first Autumn flight was on average 4,549 m, compared to 2,126 m at night.
  • For the In-Africa autumn flights, comparative figures were 3,874 m in daytime and 1,860 m at night.
  • For the Spring flights, comparative figures were 4,114 m in daytime and 1,612 m at night.

These altitudes were estimated from air pressure readings and may be underestimates. For comparison, the highest point in the Alps is 4807 m.

Peak altitudes: Some Great Snipes occasionally flew extremely high and then always during daytime. Three birds in Autumn and two birds in Spring reached 7,000 m or more. Migratory waders are able to carry out flapping flight at such high altitudes due to several physiological adaptations of the heart, lungs and muscles. The single highest altitude estimate of 8,077 m was reached in Autumn. If air pressure is accounted for this bird may have been flying above 8,000 m for five hours, perhaps reaching an altitude of 8,700 m, and coping with an air temperature of -21.3 °C. Putting this in a local context for readers: Mount Everest is 8848m high and the high points in other regions of the world are: Africa (5895 m Kilimanjaro), South America Aconcagua 6959 m, North America Denali 6190 m and New Zealand Mt Cook 3754 m.

Ambient temperature, wind condition and humidity appeared not to influence the differences in day and night altitudes chosen by Great Snipes.

Discussing the results

Great Snipe with a datalogger

The daily pattern of altitude changes for Great Snipes was very similar between Autumn, In-Africa and Spring flights, suggesting a common cause that is largely independent of climate zone (temperate or tropical), topography and landscape overflown (forest, savanna, farmland, desert or water). Altitude changes have been reported for other waders, such as Black-tailed Godwits, that have been linked to both ambient temperatures and finding more beneficial winds.

The authors discuss the possibility that landmarks are easier to see from a higher altitude when flying in daylight and suggest that predator avoidance may also account for higher day-time elevations. It would be interesting to know if a daily cycle is apparent in long flights over areas largely lacking bird predators, such as vast oceans.

There is no daily cycle in ambient air temperature or wind conditions at high altitudes that could explain the overall regular pattern of flight altitude selection found in Great Snipes but the authors discuss the theory that the warming effect of solar radiation may be countered by flying through colder, higher air. The temperatures at these heights would be too cold at night.

There are still few papers that provide altitude data for long-distance migrating birds but all of them report altitude changes and have revealed some surprisingly high flight altitudes. With more studies we may well find that migration is even more impressive than we already thought!

Paper

The full methods, results and discussion can be read in the paper in Current Biology.

Extreme altitude changes between night and day during marathon flights of Great Snipes Gallinago media: Åke Lindström, Thomas Alerstam, Arne Andersson, Johan Bäckman, Peter Bahlenberg, Roeland Bom, Robert Ekblom, Raymond H. G. Klaassen, Michał Korniluk, Sissel Sjöberg & Julia K. M. Weber.


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.

Dunlin: tales from the Baltic

Veli-Matti Pakanen, Kari Koivula  and colleagues have been studying Finnish Dunlin for nearly twenty years. These are schinzii birds that breed in coastal grazing meadows around the Baltic Sea. Several papers have been published, as you will see below, some of which are based on information collected using geolocators attached to leg-flags. Dunlin numbers in coastal Finland are dropping quickly, so this research is important to the conservation of the species. In a 2020 paper, Veli-Matti and colleagues ask whether intensive geolocator-based studies are having a negative effect on individual birds in this already-declining study population.

Global Dunlin

Up to ten races of Dunlin have been identified, which together encircle the globe. Most Dunlin spend the non-breeding season in the northern hemisphere and all migrate north in spring. The breeding and wintering ranges of the various races are summarised at the end of this blog. Here, the focus is on Baltic schinzii Dunlin, a small part of a race that largely winters in coastal North Africa and breeds in southern Scandinavia, Northern Europe, the British Isles, Iceland and southern Greenland.

According to Wetlands International, there were between 4.3 and 6.8 million Dunlin worldwide in 2015, with about one million breeding birds within Europe (BirdLife International). Whilst it is acknowledged that numbers are declining, the large range of the species means that it is still considered to be of ‘least concern’.

Different populations are faring differently. In his description of the changing Dunlin distribution in European Breeding Bird Atlas 2, John Calladine points out that there have been major losses across Europe, including Britain & Ireland, and that Baltic populations ‘are now considered threatened’. The Baltic schinzii population was most recently estimated as between 500 and 640 pairs – less than a fifth of the estimate in the 1980s. John highlights gaps in knowledge that research by the team in Finland and other groups elsewhere are helping to fill.

Migration and survival of schinzii

Dunlin that visit the UK are mostly of the schinzii and alpina races, as indicated in this map. There has been a noticable drop in the number of schinzii birds stopping off in July.

In pre-geolocator days, Ole Thorup and colleagues analysed recovery information available for Dunlin breeding around the Baltic, using 40 years of ringing data from Finland, Sweden, Denmark and Germany. At that stage there were only six mid-winter recoveries in N and NW Africa. The analysis emphasised the importance of wintering and stop-over sites in the Baltic, the Wadden Sea, SE and S England, the Atlantic seaboard of France, and the Iberian Peninsula. Paper in Ardea (2009).

Pakanen et al investigated changes in the survival rates of schinzii Dunlin nesting in Denmark, based on ringing and recaptures of a marked population. They found that annual apparent survival rates dropped from 0.817 to 0.650 between 1990 and 2006, equivalent to a doubling of the chance of dying in any given year. Paper in Bird Study (2016). The importance of monitoring survival rates is discussed in the WaderTales blog: Measuring shorebird survival.

Nests in these flat coastal marshes along the Baltic coast are increasingly susceptible to summer flooding

The use of geolocators enabled Veli-Matti Pakanen to add more detail to the migration story in the 2018 paper, Migration strategies of the Baltic dunlin: rapid jump migration in the autumn but slower skipping type spring migration. He and his colleagues showed that autumn migration is faster than spring migration, characterised by fewer stationary periods, shorter total stopping time and faster flight. The Wadden Sea was found to be an important autumn staging area for all of the tagged birds. Some birds stopped once more before reaching Mauritania. On spring migration, more sites were visited on the way north. The important conservation message from the paper is that Baltic Dunlin may be especially vulnerable to rapid environmental changes at their staging and wintering areas. (In Travel advice for Sanderling there is a suggestion that annual survival is relatively low for birds that winter in Mauritania).

In a 2015 paper in Ornis Fennica, Pakanen et al reported on the results of a single-year analysis of survival rates, concluding that there were no strong effects of leg-flagged geolocators on return rates or reproduction in schinzii Dunlin. However, they did suggest that “long term evaluations that capture the full suite of environmental conditions and assess impact on brood care are needed”. This is a question which leads us neatly on to the 2020 paper: Survival probability in a small shorebird decreases with the time an individual carries a tracking device.

Long-term tracking of individuals

To understand the range of pressures that migratory birds face, one needs to know where individuals spend their time, as was demonstrated in Spoon-billed Sandpiper: Track & Trace and Teenage Waders. Waders of a range of species have been wearing geolocators for ten or more years now, either the same devices on birds which have evaded capture, or a series of tags, when data have been downloaded and replacement tags fitted. These long-term surveys are developing our understanding of the repeatability of migratory behaviour and how birds deal with variable weather patterns, but is there a long-term cost to the individual birds that are tasked with finding out this important information?

This Dunlin wore a ring-mounted geolocator for one year, to collect movement data

Effects of tracking devices on survival are generally considered to be small. However, most studies to date have focused on birds that were caught in one breeding season and recaptured in the following season, to retrieve the geolocator and download the data. In their 2020 paper, Veli-Matti Pakanen and colleagues were able to investigate the possible accumulation of negative effects when individuals have carried the tracking devices for longer periods. Survival rates for tagged birds were compared with 338 colour-ringed birds that were followed for all or part of the period 2002 to 2018.

In the summers of 2013 & 2014, fifty-three adult schinzii Dunlin were fitted with leg-flag mounted geolocators, with a mass equivalent to 1.5 – 2.0% of body-mass. Of these birds, 17 tags were retrieved after one year and 9 after two years. Other marked birds could not be caught and carried their tags for longer periods (2 to 4 years). The research team found that Dunlin carrying a geolocator had reduced chances of survival. Their models suggest that annual survival of colour-ringed males was 0.813. For a bird that carried a geolocator for a year, annual survival probability declined to 0.748 and to 0.581 for birds that carried the geolocator for at least 2 years. Their data suggest that the reduction in survival rates was greater for females than males, even though females are larger than males.

Summer flooding of coastal breeding area is becoming an increasing problem, and likely to get worse with sea-level rise and more chaotic weather patterns

In a thorough Discussion, the authors consider reasons why tags on small waders may be reducing survival, either through ongoing stresses, impacting on things such as feeding efficiency and the energy needed during migration, or because the extra burden means that tagged birds find it harder to cope with occasional periods of tough environmental conditions. They comment on the condition of the skin under removed geolocators – something that other researchers night want to look out for.

As anyone studying breeding waders will know, nest-trapping to retrieve tags is not easy, especially if adults lose their clutches when incubation has only just started, due to flooding, predation etc. Birds may end up carrying tags for longer than intended. The authors “recommend that the detrimental effects of tagging may be avoided by developing attachment methods that are automatically released after one year, e.g. biodegradable materials”.

Balancing costs and benefits

The results from the Pakanen study of long-term survival suggest that requiring a small wader to carry a geolocator for several years may have an impact on survival. As in all mark-recapture studies, researchers are urged to assess the costs to the individual when seeking to understand what might be affecting the viability of a population.

Four previous WaderTales blogs have discussed tag effects:

Details of the Dunlin tagging effects study:

Survival probability in a small shorebird decreases with the time an individual carries a tracking device.

Veli-Matti Pakanen, Nelli Rönkä, Thomson Robert Leslie, Donald Blomqvist, Kari Koivula. Journal of Avian Biology (2020): https://doi.org/10.1111/jav.02555

Four other papers relating to this Finnish Dunlin study

Grazing by cattle is an important management tool in coastal meadows. Pakanen et al studied the impact of trampling on artificial nests and concluded that even recommended stocking rates were too high for chick numbers that could deliver a sustainable population. Paper in Biodiversity and Conservation (2011). (Redshank on British estuaries are similarly vulnerable to trampling – see Big Foot and the Redshank Nest).  

In a follow-up paper in 2016, Pakanen et al concluded that Dunlin populations could be sustained in grazed coastal meadows as long as there was no active grazing before 19 June. Meadows with grazing cattle attracted breeding birds but there was insufficient breeding success for sustainability. Paper in Ecology & Evolution (2016).

If these schinzii Dunlin chicks return to breed they are likely to try to nest nearby; something that needs to be considered when considering conservation measures

Dunlin are strongly philopatric, with both male and female chicks recruiting to suitable habitat close to natal sites. In a paper in Ibis (2017), Pakanen et al show that natal dispersal of Dunlin is strongly linked to the size of their natal site and how isolated the site is. They suggest that inbreeding may be avoided by creating a network of suitably sized patches (20–100 ha sites), no more than 20 km apart from each other. These may work as stepping stones for recruiting individuals. These results are corroborated by a 2021 microsatellite study in BMC Ecology and Evolution which shows genetic differentiation and isolation by distance within the Baltic Dunlin population.

Up to ten races

In western Europe we see three races of Dunlin – alpina, arctica and schinzii. Wintering birds are almost exclusively of the alpina race, which head north and east to northern Scandinavia, Russia and Siberia in spring. The other northern race is arctica, a very small Dunlin that breeds in low numbers in NE Greenland and possibly Spitzbergen. Schinzii has a very large breeding range, spanning the Baltic, southern Scandinavia, Northern Europe, the British Isles, Iceland and SE Greenland. There is huge variation in the timing of breeding of schinzii, as birds do not return to breeding sites in SE Greenland until the end of May, at the same time as schinzii Dunlin being studied by Veli-Matti Pakanen and colleagues in Finland will have their first young chicks.

Further east, centralis Dunlin replace alpina. Many of these birds use the Central Asian Flyway. Further east still, we find sakhalina that use the East Asian/Australasian Flyway (EAA). Two other subspecies have been identified breeding within the EAA Flyway, the more southerly kistchinski birds and actites, which breeds furthest south, on the Russian island of Sakhalin, on a similar latitude to the UK.

It is generally accepted that there are three Dunlin subspecies in North America. In autumn, arcticola head west from northern Alaska and NW Canada and follow the EAA Flyway, pacifica fly south along the Pacific coast from SW Alaska and hudsonia migrate from central northern Canada using the Atlantic Americas Flyway.


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.

Subspecies, connectivity and conservation in shorebirds

Rufa’ Red Knot in Delaware Bay

For waders such as Red Knot (Knot), conservation designations such as ‘near-threatened’ or ‘endangered’ are based upon declines and vulnerability of populations that breed in defined areas. What happens when populations mix when they are on migration or in their non-breeding areas? How do we define conservation priorities of mixed flocks? Camila Gherardi-Fuentes, Jorge Ruiz and Juan Navedo invited us to think about this issue in a 2021 Red Knot paper in Bird Conservation International.

Conservation challenges posed by overlapping subspecies

It would be convenient if subspecies of waders kept themselves to themselves but they don’t. In spring, islandica Black-tailed Godwits join limosa in Portuguese and Spanish rice fields. Icelandic populations have been increasing for a century but the Dutch population of limosa dropped by 75% between the 1970s and the period 2007-15 (as described in this blog). Which subspecies should take precedence when assigning conservation importance to a spring flock on the Tagus, or to an autumn flock in France, for that matter? These questions are not abstract; they are relevant to a decision to site a new airport for Lisbon in the estuary and to discussions about the sustainability of autumn hunting on the French coast.

Further south, in the Banc d’Arguin of Mauritania, what is the conservation importance of Dunlin? Birds from Iceland outnumber those that breed around the Baltic coast. There is no suggestion that Icelandic schinzii Dunlin are in trouble, with between 200,000 and 300,000 pairs and no indication of range change, but the Baltic schinzii population was most recently estimated as between 500 and 640 pairs – less than a fifth of the estimate in the 1980s. Does the plight of Baltic (and Irish and UK) schinzii Dunlin confer a ‘threatened’ label on the whole wintering population of the Banc d’Arguin?

Untangling Red Knot in Chile

In their paper, Insights into migratory connectivity and conservation concerns of Red Knots in the austral Pacific coast of the Americas, Camila Gherardi-Fuentes, Jorge Ruiz and Juan G Navedo present the first detailed population morphometrics of Red Knot on the southern Pacific coast of South America, during the non-breeding season, along with information about resightings of these birds throughout the Americas.

Globally, Red Knot Calidris canutus is one of the most extensively studied shorebird species and is considered as ‘Near Threatened’ at the global level (BirdLife International 2018). It is currently accepted that three subspecies are found in the Americas. The general migratory patterns are as follows but the authors of the new paper present evidence of a more complicated picture.

  • roselaari Knot breed in Alaska and Wrangel island (Russia) and migrate along the Pacific coast to spend the non-breeding season mainly in Mexico. The total population is estimated to be 17,000 birds.
  • rufa Knot breed in northern Canada and migrate down the eastern seaboard of the Americas, some travelling as far as Tierra del Fuego. The total population is estimated to be 42,000 birds. This subspecies has been designated as ‘threatened’ in the USA, where there has been an increase in the pressure upon spring staging sites. There is a WaderTales blog about the vulnerability of this subspecies, based upon work in Delaware Bay.
  • islandica Knot breed in NE Canada and Greenland and spend the winter in western Europe. Two WaderTales blogs about changing numbers of shorebirds in Great Britain and Ireland discuss declining numbers of islandica Knot.

Colour-ringing and geolocator studies that track individual birds are providing new evidence that complicates the above pattern, with some rufa Knot spending the non-breeding season on the Pacific coast of South America (Navedo, J.G. & Gutiérrez, J.S. 2019) and some roselaari wintering in Texas. Migration is even more complex, with one roselaari bird flying from Chile to Texas and then switching back west to head to Alaska (see map right). There is more about this on the Wader Study website.

The Red Knot of Chile

The team from the Bird Ecology Lab in Chile have been studying the shorebirds of the Chiloé Archipelago (42˚S, Chile) for several years. This archipelago is a Site of Hemispheric Importance for the conservation of migratory shorebirds, due to its large numbers of Hudsonian Godwit (WaderTales blog Teenage Waders) and Whimbrel.

Red Knot regularly winter in this area, with at least 150 occurring in two well-studied bays of the main island. Although it might be assumed that these birds would be roselaari, there have been colour-ring sightings of a small number of birds that had been marked with lime and green flags within the rufa flyway. With conservation of two subspecies in mind, the research team were keen to know more about the natal origins of the Chiloé Red Knot.

42 Red Knot were caught on Chiloé main island between 2017 and 2020. As well as being aged, ringed, colour-ringed with red flags, measured and weighed, blood samples were taken, in order to determine gender. The biometrics of this small sample of birds combined with sightings of red-flagged Knot has revealed a remarkable amount of information:

  • As in other Red Knot populations, males were smaller than females in all measurements (see paper for details).
  • Measurements suggest that the Chiloé population includes rufa Red Knot.
  • Weights of birds were higher at the end of April than at the start of March, suggesting an increase in body mass of between 2.9 and 3.6 grammes per day; figures that are comparable to other studies of Knot.
  • In spring, marked birds were reported in Peru, the Gulf of Mexico, Minnesota and Manitoba. These last two sightings are on the Mid-Continental Flyway, which is used by waders heading for both Alaska and Northern Canada, as might be expected of roselaari and rufa Red Knot, respectively.
  • The red-flagged birds pictured shown here were photographed by Peter Bergeson (above right) and Jean Hall (below) in South Carolina and Florida, respectively) clearly suggesting that they are rufa Red Knot.

Conservation implications

Chiloé is an important non-breeding area, where Red Knot fuel up for non-stop 8,000 km flights to the Gulf of Mexico, one of the longest migration legs for the species. Now that Gherardi-Fuentes et al have shown that these flocks include ‘Endangered’ rufa, it makes sense to provide some designated protection to the Chiloé Archipelago population of Red Knot. You can download the current Conservation Plan for Migratory Shorebirds in Chiloé.

This relatively small-scale study of Red Knot has emphasised two important points about shorebird conservation.

  • The protection of sites that hold important populations of key species provides benefits for other waders that use similar habitats. In this case, sites designated for Hudsonian Godwits and Whimbrel are being used by two subspecies of Red Knot, at least one of which is ‘threatened’.
  • Waders from one breeding population use a range of sites when migrating and during the ‘wintering’ period. Given that it is hard to know all of the possible sites that link to one breeding area, it is pragmatic to protect as many different sites as possible, across a broad range of countries. There is more about this in Spoon-billed Sandpiper: Track & Trace.
Caulín Bay in Chiloé

Paper

It is interesting that we are still discovering important information about the origins of population of Red Knot, a species that has been at the heart of shorebird research for decades. Will genetic techniques and tracking reveal more surprises? And, more intriguing, how much more is still to be discovered about less well-studied species?

Here’s a link to the paper in Bird Conservation International:

Insights into migratory connectivity and conservation concerns of Red Knots Calidris canutus in the austral Pacific coast of the Americas. Camila Gherardi-Fuentes, Jorge Ruiz and Juan G Navedo (2021).


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

Oystercatcher Migration: the Dad Effect

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

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

The story so far

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

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

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

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

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

Family ties

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

Focusing on chicks

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

Three colour-ringed chicks. Where will they go?

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

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

Results

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

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

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

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

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

What does this mean?

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

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

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

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

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

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

The broader context

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

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

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


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

Winter conditions for Whimbrel

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

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

How might carry-over effects work?

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

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

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

Life on the wintering grounds

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

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

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

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

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

A colour-ringed bird hiding in a Bijagós flock

Returning to Iceland

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

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

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

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

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

Where to spend winter?

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

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

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

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

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

Life in and amongst the mangroves of the Bijagós

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

Carry-over Effects

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

Paper

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

Previous research on Icelandic Whimbrel

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

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

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

Further reading

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

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

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

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


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

Following Sociable Lapwings

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

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

The Sociable Lapwing

Nesting close to a village

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

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

Distribution map from BirdLife International data zone

Detective work

Colour-ringed individual

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

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

Releasing a satellite-tagged bird

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

Tracked birds

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

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

Note the short vegetation

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

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

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

Three recently-fledged youngsters

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

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

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

Finding the flocks

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

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

The bigger picture

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

Post-breeding moulting flock in central Kazakhstan

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

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

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

To learn more

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

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

The paper upon which this blog is based is:

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

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

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

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

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


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

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 2020 paper shows that it is possible to trace potentially important missing sites by tracking individuals. Two 2021 papers have used data from tagged and tracked birds to update the population estimates (later in this blog) and to try to understand changes in local numbers, potentially linked to intertidal mudflats (end of this blog).

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 2020 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.

** The population total has been updated since this blog was produced. Although numbers have continued to decline, the new estimate is between 569 and 978 (details at end of this blog and in this paper).

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

UPDATE: How many Spoon-billed Sandpipers?

As discussed above, Nigel Clark, Rhys Green and colleagues previously estimated the world population of adult Spoon-billed Sandpipers at 420-456 individuals, based upon counts and sightings of individually-marked birds at a staging area on the Jiangsu coast of China. Adding in juveniles, produced an estimated population of 661-718. (Clark et al)

In a 2021 paper in Wader Study, Rhys Green and colleagues have used ten similar counts and scan samples of marked birds from China, Myanmar and Bangladesh, conducted during the period 2014-2019, to produce an updated estimate of 490 breeding-age adults (95% CL = 360-620). Adding in immature birds increases the total to 773 individuals of all ages (95% CL = 569-978). The 2021 estimate is similar to the previous one but increased geographical coverage and a larger number of surveys confer a higher level of confidence in its precision.

From the trend in the ten estimates during the period 2014-2019, it looks as if the world population of breeding adults has continued to decline at about 8% per year. This estimate of trend is not very precise but its rate is of similar magnitude to the 9% per year obtained using repeat wintering surveys in Myanmar (2009–2016). This apparent decline is less drastic than the estimated rate of loss in the period up to 2008, when there was a 26% per annum drop in the number of adult pairs across a sample of sites in the breeding grounds.

The possible slow-down in the rate of decline follows huge efforts to protect key wintering areas and staging sites, and a head-starting programme that has seen 206 chicks reared and released in the Meinypil’gyno area (2012-2020). Spoon-billed Sandpipers still seem to be heading towards extinction, but not as quickly. This emphasises the importance of finding and then increasing the protection of more staging and wintering sites, as identified in the tracking paper (see above).

UPDATE: Using local tracking information

Although tracking was primarily used to reveal the flyway-scale migratory movements of Spoon-billed Sandpipers, the finer detail of how individuals move around estuaries has proved useful too, as revealed in a 2021 paper in Wader Study about the intertidal areas of Jiangsu province in China, particularly the key site of Tiaozini. Research led by Prof Qing Chang has shown that declines in autumn numbers at Tiaozini between 2017 and 2020 appear to be associated with changes to the intertidal mudflats and positions of major channels.

Tiaozini, recently designated as part of a UNESCO World Heritage Site, is particularly important to Spoon-billed Sandpipers. An estimate of 225 birds, made in autumn 2017, represented 46% of the world population of the species and the fact that this dropped to 151 by 2020 is worrying. Most of the decline happened between 2018 and 2019. What had caused this change to numbers in a key moulting area?

To identify parts of the intertidal area used by Spoon-billed Sandpipers, the research team mapped locations of satellite-tagged birds in Tiaozini in 2017 and 2019. Data from seven tagged birds indicated that Spoon-billed Sandpipers moved to intertidal flats up to 7 km out from the seawall to feed at low tide, way beyond the limits of land-based observations. The team analysed satellite imagery and found that the extent of exposed mudflats appeared to have declined by about 20% between 2017 and 2020. The abrupt reduction in the local population of Spoon-billed Sandpipers at Tiaozini is of concern because surveys of the two closest sites which are known to support Spoon-billed Sandpipers, at Yangkou and Dongling, suggested no significant displacement of birds from Tiaozini.

It is interesting that a few tagged individuals might help to explain large-scale changes to the wader assemblage on an estuary, simply by pinpointing critical feeding areas. Although protected now, Tiaozini and other parts of Jiangsu province have seen huge changes over recent decades, with coastal land-claims and new sea walls. These may still be affecting the way that sediments form and flow within the mudflats.

The paper demonstrates the importance of securing more (and bigger) protected coastal wetlands, to provide opportunities for migratory shorebirds to adapt to change. Thankfully the Yangcheng World Heritage Site that includes Tiaozini is big and stands a good chance of being able to encompass future local Spoon-billed Sandpiper distribution change. The authors of this study stress that Yancheng-Tiaozini remains of critical importance to moulting Spoon-billed Sandpipers that will winter as far away as Banglasdesh.


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.

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.