Number of white primaries in Black-headed Gull

[Morg]

I photographed a 2CY Black-headed Gull yesterday in Stranraer, Scotland, with 5 white outermost primaries rather than 4. This may be perfectly normal variation, but reading Olsen indicates that this is a characteristic of sibiricus, though it is not really commented upon just mentioned in the descriptions of the primaries of the two forms. I wonder whether this is an oversight in the book rather than a discriminating characteristic of what appear to be very subtly differing forms.

Anyone out there looked at a lot of BHGs?

Picture on my blog if interested at http://morgithology.blogspot.com/2010/1 ... ation.html

Geoff

[adriaens]

I have not looked terribly hard at Black-headed Gulls in flight, but can find the occasional bird with 5 white primaries (P6-10) in my photographs.
Usually, P6 is whitish-grey (greyest on the inner web), but occasionally it is entirely whitish, as in the example below (another 2nd-winter bird, from Belgium).
I would not put too much importance on every word in Olsen

[little-W]

Interesting observation.
I checked my own archive of images (part of which is online), but couldn't find one individual with such a clearly white P6 or covert.

I'll keep an eye out for it.

[Morg]

Thanks for the feedback, looks like it is an uncommon variant - rather than a diagnostic feature of some sort. Surprisingly the difference was visible in the field with the bird with 5 white primaries forming a fractionally larger wedge - sort of like an inverted sabine's gull.
Nice resource little-W, will have a good look through those pics.
Geoff

[Anders]

I am curious about this topic. I just started to take pictures of gulls and this one, it seams to me, has at least three gulls with the 5th pen being white. If this is an uncommon variant, how uncommon is it then (estimated +50 BHG at the site)?