At their 'wits end?

Black-tailed Godwit might hide three semi-cryptic species within its already well-known subspecies. Photo: Steve Young (www.birdsonfilm.com).
Black-tailed Godwit might hide three semi-cryptic species within its already well-known subspecies. Photo: Steve Young (www.birdsonfilm.com).

Further evidence for a putative three-way split in Black-tailed Godwit Limosa limosa has been discovered by a team of pan-European workers.

The team, who were researching the staging and wintering grounds of the migratory wader by sampling their mitochondrial DNA, found that the two subspecies seen in Britain – Continental L l limosa and Icelandic L l islandica Black-tailed Godwits – were always diagnosable genetically and showed a clear difference in all birds sampled. This indicates that the birds' breeding populations are discrete and do not interbreed, arguably making them potentially separate species under strict interpretation of the Biological Species Concept.

Birds of known subspecies sampled on their breeding enabled the team to detect each subspecies in mixed flocks in Iberia in winter, where 6.5 per cent belonged to islandica. Previously, only the nominate subspecies – currently undergoing a rapid decline and of some conservation concern – was believed to winter there. Both forms therefore use the East Atlantic Flyway, with limosa also wintering much further south in a belt across the northern part of sub-Saharan Africa.

Höglund et al (2009) had already established that there was no detectable gene flow between all three subspecies of Black-tailed Godwit, with small but discrete genetic differences also being present in the Siberian-breeding L l melanuroides. Each subspecies is about 0.3 to 0.6 per cent different in its genetic make-up, as opposed to the clear five per cent divergence found between Black-tailed and Hudsonian Godwits.

These small but diagnostic differences – which are also matched by subtle plumage and morphometric variations – are certainly enough to distinguish between the three forms wherever they are found. Whether they are truly enough to justify the recognition of three good species is probably a matter of taxonomic ideology at present.      

Höglund, J, Johansson, T, Beintema, A and Schekkerman, H. 2009. Phylogeography of the Black-tailed Godwit Limosa limosa. Journal of Ornithology 150: 45-53.
Lopes, R J, Alves, J A, Gill, J A, Gunnarsson, T G, Hooijmeijer, J C E W, Lourenço, P M, Masero, J A, Piersma, T, Potts, P M, Rabaçal, B, Reis, S, Sánchez-Guzman, J M, Santiago-Quesada, F and Villegas, A. 2012 (in press). Do different subspecies of Black-tailed Godwit Limosa limosa overlap in Iberian wintering and staging areas? Validation with genetic markers. Journal of Ornithology DOI: 10.1007/s10336-012-0865-8