Sunday, 24 April 2011

Rufous on Wight

Swallow with rufous-washed underparts (West High Down, Isle of Wight, 20 April 2011): note the striking colour of the underparts, and that the undertail coverts seem almost as dark rufous as the face.
Just back from a week away with intermittent web access, so apologies for the late updating. First up is this interesting-looking Barn Swallow, which I found at the Needles New Battery, high up on the western tip of the Isle of Wight, on 20 April. Initial thoughts that the rufous-washed underparts might suggest an American bird can be dispelled by the dark rufous face pattern and, particularly, the thick blue breast band, which confirm it as from the Old World (in American erythrogaster, a likely split, the breast band is narrow and broken in the middle).

The thick blue breast band and dark rufous face rule out the North American form erythrogaster, which also typically shows strongly rufous-washed underparts.
So is this bird just a variant nominate rustica, or from a population from elsewhere in the species' range? Having appeared during a period of prolonged easterly winds in spring, it could potentially be a transitiva individual on appearance - this subspecies from the Lebanon, southern Syria and Israel is described by BWP as having "rusty-pink or rufous-buff" underparts, both of which could perhaps be applied to this bird. But ...

The same bird in flight, showing that the rufous washing extends fully over the underparts and underwing coverts.
... perhaps the most likely explanation can be found in another passage in BWP: "Birds from transition zones from nominate rustica into transitiva in south-west [surely south-east?] Europe and Asia Minor ... are strongly variable individually, and also outside these zones some populations are paler or darker than others, while a few rusty-bellied birds occur in almost all pale-bellied populations and vice versa." The same passage goes on to score geographic populations according to underpart colour, adding that the "proportion of transitiva-type [birds is] everywhere below 10%".

As this individual (a male) was also associating with a 'normal' adult (a presumed female), the likelihood is that it is a rufous variant rustica, perhaps from farther afield, but possibly more locally given that such individuals can crop up anywhere. I'd welcome comments from anyone who has seen or photographed similar such birds in Britain - I can't recall seeing one in Western Europe this richly coloured on the underparts.

4 comments:

  1. Hi Dominic,

    I had two such birds last Spring during a period of heavy swallow passage at Hay-a-Park Gravel Pits Knaresborough North Yorkshire. I discussed with several people and looked at BWP like you. I also came to the same conclusion - that the birds I saw were more than likely variant rusticas rather than genuine transitivas. Interesting birds to see though!

    Stephen Root

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  2. Thanks for the feedback, Stephen. Since finding this bird and mentioning it to a few people, I'm hearing more and more reports of these rufous-washed individuals. According to Martin Garner, they even seem to have been seen in the nest in Britain, which reinforces the variant theory. I gather another such bird was recently seen in Wexford, Ireland. Always interesting to see, though, as you say.

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  3. Hi Dominic,
    A similar bird seen today on Bardsey. See here-
    http://webirdnorthwales.blogspot.com
    Keep up the good work with the interesting blog.

    ReplyDelete
  4. Thanks for the comments, Marc, and interesting to see the Bardsey bird on the Welsh blog (which I enjoyed reading). I've just posted a comment there, but in short my gut feeling is that, like the Isle of Wight bird, it would probably have to be left as one of these very ocasional rufous-washed birds that seem to pop up in western populations.

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