Friday, 3 September 2010

Peep show: the verdict

Two Azores peeps, 15 October 2007. The debated bird is on the left.
If it weren't for the bill, would this peep qualify as a Western Sandpiper?
Thanks to all who commented on the identity of the Azores peep in the last post. Votes were largely divided between Western and Semipalmated Sandpipers.

Any pocket-sized Calidrid in the Azores is noteworthy, as even Little Stint – the most frequent of this species group in the islands – is classed as a rare migrant and occasional winter visitor (www.birdingazores.com). Although size is hard to judge on a single image of a lone bird, the combination of compact shape/structure and plumage characters in the image immediately suggests this is a small peep/stint. The fresh, neat-edged upperparts point to a juvenile, and the relatively long bill indeed narrows the choice straight down to Western and Semipalmated Sandpipers.

Juvenile Semipalmated Sandpiper (same as right-hand bird, top photo).

When the bird was found by visiting birders on 13 October 2007 at Lagoa Azul, São Miguel, it was identified as a Western Sandpiper – perhaps unsurprisingly, in view of the bill length. What you didn’t know from the cropped photo in the original post is that there was a Semipalmated Sandpiper standing close by. When I arrived with friends on São Miguel from Corvo on 15 October and heard about these birds, we went to the site and managed to locate them and get a few record shots. We accepted the original identification (without thinking too much about it at the time, to be honest), and one of my images was subsequently published in Dutch Birding (29: 382, plate 548) as showing Western and Semipalmated Sandpipers. To my knowledge, no objection to that identification was raised.

However, the ‘Western’ Sandpiper in that duo has recently been questioned following a debate on ID-Frontiers about a different calidrid photographed in the Azores the previous year. While checking images of Semipalmated Sandpipers online two US-based birders suggested that the long-billed Lagoa Azul bird may also be a Semi-p rather than a Western.

These additional photos of both birds, and some others for reference, hopefully set the record straight. Having looked in more detail at this species pair, my view is now that the long-billed bird is, as speculated, also a Semipalmated Sandpiper. In the image of both birds together it seems hard to reconcile them as the same species, yet if it weren’t for the bill length, would Western have entered the equation?

Although I’d seen many Western Sands before, they were wintering birds in February in the US (and also the vagrant first-summer or adult in Lothian in August 1997). When I saw my first juvenile Westerns in British Columbia the autumn after the Lagoa Azul bird, I was struck by their bright rufous-fringed scapulars, and this feature seemed pretty consistent, despite individual variation. In contrast, juvenile Semipalmateds on the same trip were more a dull chestnut on the scap fringes – as is the case with both Lagoa Azul birds.

Juvenile Western Sandpipers, British Columbia, 30 August 2008. Note
that the bird in the foreground is already replacing its scapulars by late
August. The other bird is clearly more extensively rufous on the mantle
and scapulars, this colour even bleeding into the edges of some coverts.
Juvenile Western Sandpiper, British Columbia, 30 August 2008.
With hindsight, the bill of the Azores bird, while clearly long – and indeed longer than on some cast-iron Westerns I photographed in BC – is rather thick at the base and does not seem to taper to a fine point in the classic way. This isn’t so obvious from the cropped original shot, taken when the bird has been feeding, but can be seen in the image of the two birds together. Bill length also varies according to sex, females in both species being longer billed; figure 435 in Pyle part II highlights the very subtle shape distinctions well.

Bill shape was one of the features pointed out by ‘Andy’ in his comprehensive comments, which also included reference to the bird’s moult – or rather lack thereof. A juvenile which does not yet appear to have begun moulting into first-winter plumage by mid-October, the Azores bird on this basis too seems to better fit Semi-p than the earlier-moulting Western.

Juvenile Semipalmated Sandpiper, British Columbia, 30 August 2008.
There are several other subtle features, some of them again highlighted by Andy, which are more supportive of Semi-p. These include its contrastingly dark ear-coverts, less like those of typical Western, which often has a more open-faced look. Indeed, to my eye the ‘character’ of the Lagoa Azul bird recalls photos of the famous Felixstowe stint of winter 1982-83 (see Birding World 5: 433-437 for reasons why that bird was a Semipalmated Sandpiper).

For my money, then, I am also now in the Semipalmated Sandpiper camp, and accordingly this post may be of interest to both the Portuguese Rarities Committee, Birding Azores and also Dutch Birding. Thanks again to all for their comments.

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