Tuesday, 9 September 2014

Close, but no cigar

Second-calendar-year presumed intermedius Lesser Black-backed Gull from Norway at my London study site.
During the course of many visits to my local gulling site on the Thames in east London, one of the assorted stragglers I've often hoped to find is so-called Baltic Gull, the nominate form of Lesser Black-backed Gull Larus fuscus. Identifying this dinky and declining north-east European larid is generally far from straightforward unless (a) you happen to be on its breeding grounds in far north-east Fennoscandia, or (b) you discover a colour-ringed bird which can be traced back to this core range.

Last Friday, 5th September, I got a little closer to fuscus, in spirit at least. J078K was ringed as a chick last year in Finnmark, north Norway, an area traditionally associated with Baltic Gull, but within which the other two forms of this species, intermedius and graellsii, now occur (read more about recent changes in the distribution of Lesser Black-backed subspecies here). On plumage and moult it is probably an intermedius (surely more likely than graellsii to be breeding in northernmost Norway anyway), and interestingly this bird is currently in London after spending the early winter in Portugal and then Spain.

According to the study linked above (for details of which thanks to Mars Muusse), juveniles of fuscus as well as intermedius may occur in western Europe on migration, unlike the more easterly-migrating adults. Returning youngsters in their first spring are now known to be identifiable through primary moult, so in the absence of a colour ring birds of this age are the best bet when searching for candidates. My own search goes on, but in the meantime here's the low-down on J078K. (Thanks also to Peter Rock, Ronald Klein, Frode Falkenberg and Detlef Gruber for contributing useful comments and information on this).

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