Birdwatchers and farmers plot range-changes of Black-tailed Godwits
A recent paper by Igor Popov and Dmitry Starikov in Wader Study, the journal of the International Wader Study Group, provides a glimmer of good news for those concerned about the huge losses of the nominate limosa subspecies of the Black-tailed Godwit. At the same time as limosa numbers in the west of the range have been dropping by an average of 5% per year, there has been colonisation of areas of Russia that are beyond what was thought to be the northern edge of the subspecies’ range. Over a similar time period there has also been a well-documented range expansion of the islandica subspecies, about which more later.
Black-tailed Godwit is classified as near-threatened by IUCN/BirdLife, as a result of widespread and rapid declines in numbers of limosa, the most numerous subspecies (Gill et al 2007). These declines have been linked to agricultural intensification and changes in the timing of farming operations on grass fields in the breeding season, habitat changes and the destruction of wetland habitats in Europe and western Africa, where limosa birds spend the winter, and possibly hunting effects. In contrast, the Icelandic subspecies has been increasing. Tómas Gunnarsson and colleagues had previously mined long-term datasets, provided by Icelandic farmers, the Icelandic Natural History Institute and others, to show that the range of the islandica subspecies has expanded hugely over the last century. Now Igor Popov and Dmitry Starikov have used similar detective work to show that the northern edge of the limosa subspecies is moving north.
In some ways, the Russian research is quite conventional, in that the records upon which the study is based were collected by scientists and birdwatchers. The region under consideration belongs to five administrative areas of the Russian Federation but the focus is the area surrounding St Petersburg, where reports go back to at least the end of the 19th century. By delving into the records from the libraries of the Russian Academy of Sciences, the Russian National Library and the libraries of various local institutions, the authors were able to pull together a list of observations and to establish that Black-tailed Godwits were absent from other lists. At the heart of the study is the Nizhnesvirsky Reserve where systematic observations have been made for fifty years.
In the late 1980s, four pairs of Black-tailed Godwits were observed in the Nizhnesvirsky Reserve with other records between 1997 and 2003. At the same time, there were increasing numbers of sightings in the wider study area and from beyond its borders, where there had been reports from as early as the late nineteenth century through to the 1940s and 1950s, with the first breeding record in the 1970s. There is now a small but apparently stable population in the reserve, an area in which mean April temperatures have risen from +2.2°C to +4.8°C over the period 1880 to 2015. Within the larger study area, Igor Popov and Dmitry Starikov feel that it is likely that there have been similar colonisations in other locations, as birds have settled in small numbers within dispersed areas. One factor that may have contributed to the ability of Black-tailed Godwits to expand their range northward in recent years is the replacement of large areas of the taiga forests across the whole of Northern Russia with more open habitats that suit the species.
The documentation of the range epansion of islandica Black-tailed Godwits in Iceland owes more to the inquisitive nature of Icelandic farmers than to the observations of birdwatchers. This is fortunate, as farmers operate throughout Iceland, whilst birdwatchers are few and far between. As the species spread into new coastal areas, farmers could not help but notice the arrival of these noisy russet-red birds, feeding in hay fields, perched on fence-posts and careering around the skies in their acrobatic display flights. The key thing that farmers did was to tell someone. Many of their observations ended up at the Icelandic Institute of Natural History in Reykjavík, which encourages and collects submissions of natural history records from across Iceland. Tómas Gunnarsson collated these records, together with others, in order to date the major patterns of colonisation of breeding sites by black-tailed godwits. In total, 118 records were obtained from these sources, which enabled identification of dates of ﬁrst or recent breeding for 65 individual breeding sites within 39 individual basins throughout Iceland. The earliest breeding date of these sites was used as the colonisation year for each basin and the general pattern of colonisation is summarised in the figure below.
As in Russia, one of the drivers of the increasing Black-tailed Godwit population in Iceland could well be changes in spring temperatures. In this blog about the effect of temperature and volcanic eruptions on breeding success, there is a clear relationship between the number of successful broods and the temperature in May, as you can see in the figure alongside. You can read more about this in the paper:
Effects of spring temperature and volcanic eruptions on wider productivity. Tómas Grétar Gunnarsson, Lilja Jóhannesdóttir, José A Alves, Böðvar Þórisson & Jennifer A Gill. IBIS (2017) DOI: 10.1111/ibi.12449
There was an even warmer spring in 2017 – which explains the orange dot (top-right) in the figure above. There’s more about wader research in Iceland during the summer of 2017 in this blog.
Conservation implications of range expansion
Numbers of the islandica race of Black-tailed Godwits are still rising but their European cousins (limosa) are in serious decline, especially in the Netherlands. This blog reveals a 75% decline in numbers since 1967 and concludes with: “Although enormous amounts of money and effort have been expended to conserve continental godwits, our findings make clear that these have been ineffective or insufficient.”
The recent colonisation of new areas in Russia does not necessarily mean that the limosa Black-tailed Godwit will become abundant in its north-eastern territories. It is still rare, and its numbers are only increasing slowly. In Finland, which lies at a similar latitude, the breeding population was estimated at 20 pairs in the 1980s, 25–35 pairs in the 1990s (Vaisanen et al. 1998), and 40–60 pairs in the 2000s (Jensen 2007). Such detailed estimates are not yet possible for the new breeding areas in Russia but, because all reports concern only small numbers, Igor Popov and Dmitry Starikov conclude that no rapid population growth has taken place to date. Sadly, it appears that colonisation of northern areas is unlikely to be much compensation for losses elsewhere in the limosa range.
To read more about the Russian range expansion:
Popov I. & Starikov D. 2015. Recent northward expansion of breeding Black-tailed Godwits Limosa limosain NW Russia. Wader Study122(3): 173–183.
Icelandic colonisation data are used in five papers:
When Icelandic farmers sent in their Jadrakan (Black-tailed Godwit) observations to the Natural History Institute the term ‘citizen science’ had not been invented. Nearly 100 years after the first records, their sightings have not only chronicled the spread of the species, they have also facilitated the publication of some interesting – and varied – papers.
Double buffer effect: As the population of Icelancic Black-tailed Godwits has increased, birds have moved into areas of poorer quality breeding habitat as well as areas of poorer quality winter habitat. Gunnarsson T.G., Gill J.A., Petersen A., Appleton G.F. & Sutherland W.J. A double buffer effect in a migratory shorebird population. J Animal Ecology 2005, 74:5 965-971.
Seasonal matching: Black-tailed Godwits that breed in newly-colonised, poorer-quality breeding habitats tend to winter in poorer-quality wintering sites. Gunnarsson T.G., Gill J.A., Newton J, Potts P.M. & Sutherland W.J. Seasonal matching of habitat quality and fitness in a migratory bird. Proc. Biol. Soc. B 2005 Nov 7; 272(1578): 2319–2323.
Arrival times in spring: Individual godwits from traditionally used breeding areas, where average habitat quality and spring temperatures are higher, arrive in Iceland earlier than those which breed in recently occupied areas, where average habitat quality and spring temperatures are lower. Gunnarsson T.G., Gill J.A., Atkinson P.W., Gélinaud G., Potts P.M., Croger R.E., Gudmundsson G.A., Appleton G.F. & Sutherland W.J. Population-scale drivers of individual arrival times in migratory birds. Journal of Animal Ecology 2006 75, 1119–1127
Selection pressure: The size of male Black-tailed Godwits is highly variable and varies strongly in relation to the timing of colonisation across Iceland, with small males being absent from recently-colonised sites. This is most likely to be a consequence of preferences females may have for small males (and good quality habitats). Gunnarsson T.G., Sutherland W.J., Alves J.A., Potts P.M. & Gill J.A. Rapid changes in phenotype distribution during range expansion in a migratory bird. DOI: 10.1098/rspb.2011.0939
Migration strategies: Individuals experiencing more favourable winter conditions had higher survival rates, arrived on the breeding grounds earlier, and occupied better quality breeding areas, even when migration costs are substantially higher. Alves J.A., Gunnarsson, T.G., Hayhow D.B., Appleton G.F., Potts P.M., Sutherland W.J. & Gill J.A. Costs, beneﬁts, and ﬁtness consequences of different migratory strategies Ecology, 94(1), 2013, pp. 11–17
WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research. Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.