Friday, 23 November 2012

Colour-ringed intermedius

First-calendar-year Lesser Black-backed Gull of the subspecies intermedius. This individual was ringed as a chick in north-east Denmark in June this year. Note the new first-winter mantle and scapular feathers.
Lesser Black-backed Gulls are a very familiar sight in London, where the subspecies graellsii has a small but increasing breeding population, with far larger numbers in winter. Smaller numbers of intermedius-type birds also occur outside the breeding season, and are best identified in adult plumage when their blackish upperparts stand out in contrast to the dark lead-grey of graellsii. Identifying intermedius at other ages is much trickier, if not sometimes impossible with complete certainty, and it has been suggested that the two subspecies may represent only one clinal taxon (Olsen and Larsson 2003).

I found the above first-winter Lesser Black-backed Gull on 16 November on the Thames at Rainham, and was immediately struck by its unusually pale head and underparts contrasting with darker upperparts. Only after I started photographing it did I realise it was sporting a smart blue colour ring. I've seen blue-ringed Lesser Black-backeds from the Low Countries here before so forwarded details to a scheme there, only to be told it was in fact a Danish ring.

V.MOL reveals a rather strongly barred rump and uppertail, among other features.
Thanks to a prompt response from Kjeld Tommy Pedersen, I now know that V.MOL was ringed as a chick on the Danish island of Hirsholm, in the Kattegat between Denmark and Sweden, on 26 June this year. Geographically this is close to the edge of the range of intermedius in southern Scandinavia; head south-east into the mouth of the Baltic from here and nominate fuscus ('Baltic Gull') takes over. This was not only my first colour-ringed Danish gull, but also welcome confirmation from a British perspective of the appearance of first-winter intermedius.

UPDATE Today (26 November) I found V.MOL again at the same site - remarkably among thousands of gulls in the area - and it was within 100 m of where I first saw it 10 days ago! It spooked quickly but I managed to fire off this shot to show the underwing pattern, something I wasn't able to observe last time.

Ten days later, here is colour-ringed intermedius V.MOL again, showing off the axillary and underwing pattern.
I've also created a Google map to show the distance between ringing and observation sites - 588 miles in this instance. I'll be plotting further colour-ringed Lesser Black-backed Gull sightings on this map in due course.


View Lesser Black-backed Gull in a larger map

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