Monday, 2 March 2009

Continental drift

As I stepped out of the house this morning in Muswell Hill to head to work, a Coal Tit was calling in the birch tree opposite - a decent garden bird, as at best we tend to get one or so a month. I then picked up another one much closer in next door's beech tree, and two more up high, along with a single Blue Tit.

Four together was exceptional, so I paused to eyeball the closest one in the beech. At 15-20 ft away, I could see it clearly had bluish-grey upperparts with no hint of olive or brown, indicative of the nominate continental subspecies. In fact, in excellent light the colour was quite striking and obviously different. Overall it was a smart-looking bird, with bright white cheeks and nape patch contrasting against the black of the head (though with a slightly messy 'bib'), and flanks strongly suffused buffish. Looking at the other birds from underneath and more distantly, it was hard to be certain of their upperpart colour, but I suspect it was likely that some, if not all, were also continental birds.

They were on the move and so was I, but I headed home again at lunchtime to try and relocate them. Needless to say, having been actively feeding and on the move when I saw them earlier, they had passed straight through.

The key field character for this subspecies is the bluish-grey upperparts, while the underparts seem more variable. According to Tits, Nuthatches and Treecreepers (Harrap, 1996), for example, "Fennoscandian and western Russian birds (south to NE Poland and the northern Carpathians) ... [have] flanks to undertail coverts grey-buff", while these areas are darker on birds from central and western Europe which, in extreme cases, "approach britannicus". The tone is on "average more cinnamon (less grey)" on birds from Italy and Sicily, and so on, in assorted permutations according to freshness of plumage and, doubtless, individual variation.

The Migration Atlas indicates that Continental birds reaching Britain do so from the near Continent mainly via the east and south coasts, so a western/central European origin might be most likely for nominate birds occurring in the London Area; the few ringing recoveries in Britain of nominate birds all involve individuals originally trapped in the Low Countries and Germany. Interestingly, and a fact I didn't know before today, Continental Coal Tits bred on Scilly between 1976 and 1989.

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