Black-tailed and Bar-tailed Godwits

Key featured species

• Black-tailed Godwit Limosa limosa
• Bar-tailed Godwit Limosa lapponica

The problem

Although these two godwits are readily distinguishable in flight, in winter they are superficially similar when on the ground.

The solutions

Status

Bar-tailed Godwit is a more northerly breeding species than Black-tailed, its summer range extending from northern Scandinavia eastwards across the tundra of northern Russia. Western breeders commonly winter in Britain, where the population has remained fairly stable since the 1970s with 46,000 counted in 2003-04 (Collier et al 2005). Small fluctuations in the numbers are apparently related mainly to weather conditions in the Wadden Sea in The Netherlands.

Breeders in central Siberia, however, undertake a huge migration to and from western Africa. Their winter range extends right down to South Africa, but the largest concentration – about half a million – occurs on the Banc D’Arguin in Mauritania. It is these African winterers that are responsible for a marked easterly passage up the English Channel in late April and early May, about a month after the departure of the bulk of our wintering birds.

The Black-tailed Godwits that winter in Britain are of the Icelandic race islandica, which in summer is a deeper orange than the nominate continental race. The latter breeds in eastern England in small numbers but is otherwise scarce as a passage bird, and it too heads off to West Africa in winter (see Birdwatch 154:18-20 for a discussion of their separation). Unlike Bar-tailed Godwit, Black-tailed has increased spectacularly as a winter visitor, from approximately 100 in the1930s to a current peak of about 30,000.

In flight

Separating the two species in flight is easy. Black-tailed has a striking white wing stripe, framed in black, and a square white rump that contrasts with its black tail. Its underwing too is white, and again is framed by black leading and trailing edges. In addition, Black-tailed is a sleek, elongated bird in flight, its long legs protruding well beyond the tail and counterbalancing its long neck and bill.

Bar-tailed is stockier-looking when flying, with shorter legs that barely extend beyond its tail. In plumage, Bar-tailed resembles a Curlew or a Whimbrel, being essentially brown with a barred tail; most significantly, it lacks a wing-bar and shows a white ‘V’ up its back. The underwing is plain whitish.

Bar-tailed Godwit is in fact more likely to be confused with the similarly sized Whimbrel, particularly in spring when small numbers of the latter often tag onto migrating flocks of ‘Bar-wits’ as they head up the English Channel. When its decurved bill isn’t apparent, Whimbrel can often be picked out by its ‘head-up, crop-heavy’ appearance, whereby the upper breast seems to bulge more, and in a direct comparison Bar-tailed is seen to be slightly smaller and slimmer-winged. Whimbrel has darker, more uniform plumage tones than Bar-tailed, which is paler above with darker, contrasting primaries and whiter underwings.

Another pointer is that whereas Bar-taileds often form large and purposeful flocks, Whimbrel tend to form small groups or straggly lines. When heard, Whimbrel’s descending seven-noted whistle is an instant give-away.

On the ground

Distinguishing between the two godwits on the ground is a different matter, and here shape and structure come into play again. Bar-tailed is a shorter-necked, shorter-legged and stockier-looking bird than Black-tailed, with an upward curvature to the bill that is visible in closer views. Black-tailed is much more elegant, being longer-billed and longer-legged.

To separate them in winter plumage, look first at their upperpart patterning: Black-tailed is uniformly plain smoky grey, whereas Bar-tailed has strongly variegated upperparts with prominent pale feather fringes. (It is always useful to think of Bar-tailed as having upperparts like a Curlew.) Bar-tailed also shows a longer, more prominent supercilium.

Calls

Black-tailed Godwit has a variety of calls but in flight it usually gives a rather soft kik or kik-ik, which may sound conversational in a flock. It is sometimes elongated into a more musical kik-ik-ik-ik. Bar-tailed’s call is a rather distinctive, mellow and rhythmic ik-ik, which is loud and emphatic compared with that of Black-tailed, although it too may be elongated into an ik-ik-ik-ik.

Handy hints

Although this article is concerned mainly with the identification of Black-tailed and Bar-tailed Godwits in winter, the following points are also worth remembering.

Juveniles

In both species the juveniles show neat, immaculate plumage in late summer and early autumn, unlike the adults which are usually in a rather messy state, showing a patchy mixture of moth-eaten deep orange summer plumage and fresh grey winter feathering. Juvenile Black-taileds are finely scalloped above, whereas juvenile Bar-taileds, like adults, show variegated upperparts similar to those of Curlew. Juvenile Bar-taileds are warm buff below, in contrast to juvenile Icelandic Black-taileds, which are quite a bright, rather deep orange. In fact, the brightness of their plumage often confuses people into thinking they are summer-plumaged adults.

Spring moult

In spring, our wintering Bar-tailed Godwits depart in February and March to moulting grounds on the Wadden Sea and thus usually do not acquire summer plumage before their departure. In contrast, the West African migrants that appear a month later will have largely moulted into summer plumage.

Summer plumage

Male ‘Bar-wits’ in summer are stunningly attractive, being uniformly and evenly dark chestnut-red below. Summer females, however, remain ‘winter-like’: most are largely white below, although many acquire a scattering of rufous-cinnamon feathering and others show a paler pinky buff or cream coloration, as well as some delicate grey streaking and barring. Adults can thus be readily sexed in spring, but note that the first-summer birds of either sex that remain in their winter quarters acquire very little summer plumage (Cramp and Simmons 1983).  

Bill length

In both species, the bill of the female is longer than that of the male. Female Bar-tailed’s bill is about 20 per cent longer, and female Black-tailed’s is 12-15 per cent longer.