Friday, 2 October 2015

Baltic Gull, Lincoln

I was in Lincoln today, so decided to call in for a look at the putative adult Baltic gull Larus fuscus fuscus at Apex Pit. It's a small race of lesser black-back with a pure white head, smaller bill, a darker mantle (even darker than great black-back), obviously longer wings projecting well past the tail and primaries completely black except for a tiny white mirror on P1. No sign of any primary moult. Quite a smart looking bird.

The identification challenges of L.f.fuscus are discusssed here. Although it is pretty straight forward to separate this race from the typical race we see in Britain (L.f.graellsii), it is more difficult to separate it from L.f.intermedius which breeds in western Scandinavia but also occurs in Britain, especially in winter. Something like 15% of intermedius are dark enough to look like pale fuscus. However, the Lincoln bird meets most of the identification criteria for an adult fuscus as defined by fuscus expert Lars Jonsson, i.e. 1) unmoulted inner primaries, 2) a white unspotted head and 3) dark blackish upper parts. Only the brownish hue to the scapulars is missing, but at the distance the bird is being observed, at dusk, this is impossible to see (at least it was this evening).
 
Unfortunately it's so far only ever seen at the roost which means the light is very poor when it is present. It's a nice view through the scope, good enough to see the tiny mirror on P1,  but almost impossible to photograph.  In the photo below it's the third bird from the left. This photo was taken at sunset at a distance of about 400m, but even so it shows well the small size and long primaries.There is a nice comparison betweeen the this bird and the extreme left bird which is a graellsii

Thanks to Ben Ward for showing me round and getting me onto the bird.



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