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.
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.
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.
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.
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.
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.