Wednesday 17 February 2010

First-winter Slaty-backed Gull - a bit of a banana-skin?

One of the main objectives of a recent trip to Japan (Dec-Jan 2009/10) was to learn something about the identification of young Slaty-backed Gulls. But is seems that they are something of a banana-skin. This post shows a selection of birds that share certain character traits: uniform greater coverts which form a distinct panel, plain tertials, simply patterned second generation scapulars (with dark shaft streaks rather than cross-bars, and often greyish in tone), wholly dark tails and a well barred rump and upper tail coverts (more or less like smithsonianus). Most also have a dark eye mask and relatively pale primaries (often similar in tone to the tertials) which have rather broad pale fringes. Yet despite these similarities, there are dramatic differences in the overall plumage tones and general appearance: they range from uniformly dark looking (like a dark smithsonianus) to uniformy pale looking (like many Glaucous-winged Gulls), while some have a contrasting mixture of dark and pale tones. I came away thinking that they surely all can't be Slaty-backed Gulls, but at the same time conscious that they share strong similarities. The problem of course is that very little is published on these birds, and I don't know of any papers that deal explicity with the variability of first-winter Slaty-backed Gull (though of course there are a few photos in the standard gull texts).

The key question is whether all of these birds would be considered identifiable/acceptable as Slaty-backed Gulls in Europe or N America. With vagrants we tend to be rather strict with acceptance criteria, accepting only the most typical birds; if these birds are all Slaty-backed Gulls, then just what is a a 'typical' Slaty-backed Gull? My feeling is that perhaps we should actually be thinking of them in terms of plumage 'types'?

I'm very much out of my comfort zone here and not at all sure about the identity of a number of these birds. Hence, the objective of this post is not to illustrate lots of bona fide Slaty-backed Gulls but simply to put some pictures of gulls on the net, in the hope that they are interesting, useful and lead to informative discussion. If some of these birds are hybrids (e.g. Slaty-backed x Glaucous-winged is a distinct possibility with some of the paler ones) then what features should we be using to seperate pure from hybrid individuals?

I'd love to hear views on these birds from anyone with experience of Slaty-backed gull, and especially ideas on where to draw the line between pale end Slaty-backed and hybrids with Glaucous-winged.

In the field I asked some local birders about some of these birds and they indicated that they were indeed Slaty-backed. However, detailed converstions were difficult because of language.

I've arranged the photos in a continuum, from dark to pale birds; the contrasting ones are somewhere in the middle.

This bird, and the one below, cause most concern. Are they pure Staly-backed Gulls, but simply extremely pale ones, or are they hybrids involving Glaucous-winged Gul?

Some flight shots are presented below. The key features are the smithsonianus-like rump and tail pattern, the rather uniform primaries (with none of the strong patterning (spots, bars) so evident in P1-5 of Vega and Herring Gulls of this age) and the uniform panel formed by the greater coverts. The underwing coverts are very uniform, softly patterned with brown.

I noticed that in the paler birds, the cetral part of the rump is paler than the lower back and UTCovs and so forms a pale band; this is particularly clear in this bird.

This is the same individual as show in the picture above.

Sunday 14 February 2010

Iceland Gull (3cy) Peterhead

13 and 14 Feb were very quiet again at Peterhead, with only the longstaying second-winter Iceland Gull being of any note. Its iris is clear yellow, although you have to zoom into the images to see this properly.

Tuesday 9 February 2010

Owls and Caspian Gulls in Latvia

I spent 4-8 February birding in Latvia, with Paul Baxter, Hywel Maggs and Phil Crockett. We spent time in the forests around Riga looking for woodpeckers, but also managed to catch up with a Hawk Owl that had been around for a week or so (130 km SE of Riga) and a Ural Owl that was frequenting a city centre park in Riga. And of course we also had a day on Riga dump, looking at Caspian Gulls.

Ural Owl, Riga city

Pygmy Owl.
Pygmy Owl; a lucky flight photo

Caspian Gull (3w)

Caspian Gull; same bird as above
Caspian Gull; same bird as above, long-calling in the classic albatross posture
Caspian Gull; a large, presumably male bird.

Caspian Gull. Same bird as above. The bill colouration, rather short P10 tongue and black across the tip of P10 suggest that this bird is not fully mature.

Caspian Gull.

Caspian Gull; same bird as above. This bird has some black in the primary coverts, just visible here. Also note that the black extends inwards as far as P4.
Presumed Caspian Gull. This 3w bird called like a cachinnans, but one or two things concern me a little. Its bill is rather bright and, especially visible in the image below, bulges at the gonys; it also has rather a lot of neck streaking. Collectively, these features make it a less than typical bird. If I was in UAE, without the call I would just take this to be a barabensis.
Presumed Caspian Gull; same bird as above