Friday, 1 April 2011

Uncommon gulls?

Second-calendar-year Common Gull Larus canus (Rainham, Greater London, 11 March 2011). As well as the dense brown spots, bars and chevrons on the head, neck and flanks, note also the obvious patterning on the uppertail coverts. This individual, uniquely among all the first-winter-type Common Gulls I've photographed recently, shows strongly barred Eurasian Curlew-like axillaries, suggested by Olsen and Larsson 2003 as indicative of heinei.
I spent the afternoon on Rainham tip today, but it was a fairly fruitless endeavour. The hordes of winter gulls present less than a month ago have now largely dispersed, and though at times several hundred gulls were in the vicinity, they rarely came in to feed today. Single second-calendar-year Caspian and Yellow-legged Gulls were the only noteworthy larids other than the common five species. Even Common Gull itself was represented by just a single fly-over adult in breeding plumage - a far cry from previously.

This last species has become a focal point in recent weeks. I noticed a post on Martin Garner’s blog (see links below) back in December about Common Gulls of the subspecies heinei, in which he flagged up the possibility that this Russian form might occur here more often than is suggested by the very few records (which appear to be related to ringing recoveries). When we hosted the Rainham gull day in early March Martin again talked about heinei and ran through characters indicative of this form.

Second-calendar-year Common Gull L canus (Rainham, Greater London, 11 March 2011) - same individual as above. This flight shot shows not only the strongly barred axillaries and dark-tipped uppertail coverts, but also that the undertail is similarly patterned with dark chevrons. This bird was very striking on the wing.
In several gulling sessions since then, I’ve looked a lot more closely at Common Gulls than usual, and photographed several dozen. I’m not certain that I’ve come close to a true heinei yet, but I have seen several birds – first-winter, second-winter and adult – which have shown some Russian-type characters. What I’m less certain of is how much overlap in these features there is between nominate canus and heinei.

Second-calendar-year Common Gull L canus (Rainham, Greater London, 11 March 2011). A different individual to above, this bird has intermediate patterning on the axillaries, with only the tips showing any dark notching.
Second-calendar-year Common Gull L canus (Rainham, Greater London, 11 March 2011). Other differences between heinei and canus of this age quoted by Olsen and Larsson 2003 include darker and deeper brown upperwing coverts and generally darker brown lesser coverts, creating a stronger dark leading edge to the inner wing. Doubtless such differences are affected by wear and moult, and perhaps less useful by spring.
Nominate canus breeds in north-west Europe from Iceland, Britain and France east to Moscow and the Kola Peninsula, overlapping and apparently integrading in the east of its range with heinei. This subspecies replaces canus eastwards in a wide swathe towards the range of kamtschatschensis, which breeds in the Russian Far East (and which is also very probably a separate species). Birds with mixed canus and heinei characters don't make field identification straightforward, and according to Olsen and Larsson 2003 this is "impossible in all but large birds". Things seemed to have moved on a little in the last eight years, however, and advice which may help reliably distinguish heinei at all ages is said to be in preparation - more in due course (I'll provide links to documentation as and when it becomes available).

On the Rainham gull day with Martin Garner in early March we also observed a Common Gull still largely in juvenile plumage (too distant for photography, unfortunately). I have occasionally seen juvenile plumage retained late into the winter in Common Gulls. This presumably happens for a variety of reasons affecting individual birds, and is not related to subspecies, but the following shots are included here for reference:

First-calendar-year Common Gull L canus (Prague, Czech Republic, 29 December 2008). A striking bird in this plumage in mid-winter, with heavy brown blotching on a white background. Photographed going to roost at dusk.
First-calendar-year Common Gull L canus (Prague, Czech Republic, 29 December 2008). The same bird as above, resting briefly on the water, allowing its retained juvenile scapulars to be seen clearly.
Second-calendar-year Common Gull L canus (Alexandra Park, Greater London, 17 February 2008). Even in this shot which was taken into the glare of strong sunlight, the heavy streaking around the head, neck and underparts, and the juvenile scapulars, can clearly be seen. This bird also appears to have an odd, 'snouty' bill profile.
To close on this topic for now, here are some Common Gull links that may be of interest:

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