Saturday 30 March 2013

adult Thayer's Gull photoshoot

It is now or never on this one, as later today I head off to Iceland hopefully to see Iceland and Glaucous Gulls in good numbers so I'll try and do the odd post from there if I get the time. Anyway, I was hoping to do a post from yesterday when I went to Thetford and saw the (sort of) Black-bellied Dipper and a couple of Otters in the river. But, to cut a long story short, the day was grey, there were loads of people and the whole scene just didn't fill me with much enthusiasm to spend much time there nor write much about. Seems like everyone else has enjoyed their time in Thetford, so fair play.

So let's get back to the job in hand - adult Thayer's Gulls. Like the other ages, and as you'll see below, they are structurally very variable and you have to watch out for American Herring x Glaucous-winged Gull hybrids too. However, what seems to hold true is that on all birds P10 is pale tipped with an indistinct dark subterminal band, with the black on the outer web extending to the primary coverts, a mirror on P9 with black running through the leading edge (this mirror seems more extensive in the field on more individuals than literature suggest) with P6-P8 having pale-tipped tongues. P6 has a nice subterminal band, and on quite a few individuals P5 is unmarked (though on some there is a smudge of dark on the outer web of this feather). Once again, all the photos here are taken 16-23 February 2013 in northern California.
notice the short-legged appearance, dark eye and tepid bill colour. Structurally, too, this bird is quite squat and would be labelled in the 'classic' bracket of this species.

A more snouty individual with a pale eye - see the two images below for the same bird. Note the bright pink, relatively short legs and relatively dark grey mantle.

Purplish-pink orbital ring, tepid bill and even though the eye appears pale there is still some speckling present.

Thayer's Gulls have a very pale looking underwing, with dark markings restricted to the tips of the outer primaries. The leading edge of P10 shows a darkish tongue.

A typical individual, looking quite Iceland Gull-like in its facial expression - though note the dark iris

Same individual as above and below, illustrating a relatively well-proportioned looking gull

Just like a pale iris isn't always wholly pale, good views of a gull with a dark iris from a distance show paleness on closer inspection. Note the peppering in the iris of this bird; its orbital ring is pretty indistinct but it is purplish pink.

Quite a nice pose here, illustrating the upper and under primaries on a pretty classic looking bird - though many birds showed a more extensive mirror in P9 than I was expecting. This bird was no exception - the white mirror protudes well onto the outer web though is still bordered by black on the leading edge. Also note how on P9 and P10 the black tongue goes up as far as the primary coverts.

Another photo of the bird above.

A pretty classic looking, presumably female Thayer's Gull. This is the image of the species I grew up with, but there is far more variability in this species which presumably means that in a WP context, not all vagrants are being picked up.

A paler-eyed, longer billed individual to the bird depicted above. Again, note the distinctive nape hue and darkish grey mantle

A heavy-billed individual with a pale eye, though this is still peppered by dark spots. The rich pink legs and short tibia are typical of Thayer's Gull.
And finally for this post, watch out for imposters such as this bird - presumably an American Herring x Glaucous-winged Gull. They're pretty common in California, so must be pretty common in the Arctic regions where they interbreed. So, although unrecorded as a vagrant to Europe, they shouldn't be discounted: -

Glaucous-winged x American Herring Gull - note the rather dopey look and smudging akin to Glaucous-winged Gull and the paler mantle compared to Thayer's Gull.
same bird as above - very Thayer's-like primaries (though a large P10 mirror is almost tipped and note the extensive dark on the undersides of P7-10).

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