Swift spp ID, Cornwall, UK (1 Viewer)

[Ilya Maclean]

I found this unseasonal Swift in Cornwall yesterday, and after scrutinising it for about 40 mins aware that Plain Swift is not beyond the realms of all possibility, couldn’t really turn it in to anything other than Common Swift Apus apus, although the dark throat was quite puzzling. However, after posting photos on social media etc, a few folk have suggested I might have been a bit hasty to dismiss it.

I suspect, given photo quality and light conditions, available evidence is inconclusive, and Occam’s razor has to apply. Certainly poo or a good sound recording would be more convincing than these. But at very least, I thought this might provoke a bit a bit of a debate about what the good ID features for Plain Swift really are, and whether a British record is really that bonkers given e.g. extralimital records in northern Spain.

 

[Jon.Bryant]

Just refreshed my memory by re-reading the article in Dutch Birding on the birds discovered in Spain.

The features they used to confirm the ID were rather limited, and were
1/ Lack of pale throat. Interest they mention that worn Common Swifts occasionally also have a dark throat - but according to BWP Swift's complete the moult of the head and body feathers in Jan to March, so a spring bird should be fresh rather than worn.
2/ Vocalisations
3/ Wing span. This was assessed by photographing the birds immediately adjacent to an object of known size, and using software to then calculate the wingspan. Obviously there is nothing in your photos to allow this to be done. Wingspan of Plain is 36-39cm and Common 40-44cm, so a small Plain, may be noticeably different.
4/ More erratic flight, with more active wing beats and less gliding. This was 'proven' to be more that just a feeling, by video analysis of feeding of Common Swift and Plain Swift in similar weather conditions. This is also mention in the Collins Guide.

Your birds looks interesting, but I suspect that it will just have to do down as an early Common Swift...

...as it was posted after midday, I assume It wasn't an April Fool?

 

[Bubbs]

Plain Swift discovered breeding in mainland Portugal

Paulo Belo outlines a remarkable range expansion for a species thought previously confined to Macaronesia as a breeder.

www.birdguides.com

 

[Ilya Maclean]

Not an April fool's. It was found in March!

On balance, having done a little more homework on this and having consulted more widely, I think this is a Common Swift, which should be the default choice anyway (aside from Pallid or Alpine, which this clearly isn’t).

In addition to breeding in mainland Portugal, there is a recent extra-limital record from Faro de Cabu Peñes in Asturias in northern Spain. It is definitely one that UK birders should be looking out for! I post the following, partly for that reason.

My reasons for thinking this is a Common Swift:

• Throat patch. Although it’s remarkably dark-throated, in an adult swift, which this is, the throat patch on a Plain Swift is generally smaller, being restricted primarily to the chin rather than throat. Though this does not seem to be a 100% reliable feature, if you lighten the third photograph, you can see the shape of the throat is, to my eye pretty much what you'd expect to see on a common swift in terms of shape (albeit uncharacteristically dark).
• Head shape. Though not really mentioned much in the literature, looking at quite a few photos and recalling birds I have seen on the Canaries and in Madeira, this seems to be quite a distinctive feature. Plain tends to have a small bill and steep forehead giving them quite a bulbous headed appearance. This bird has a pretty classic common swift head shape.
• Colour – though not discernible on photos, in the field the bird was more black-brown rather than dark grey brown, which favours Common Swift.
• Flight style. Within range, and in the absence of hearing them call, this is the most distinctive feature. Plain has a fluttery, faster-winged beat flight style vaguely reminiscent of Little Swift. Of course, this is always a little subjective, and a tired, vagrant bird might be expected to be more languid, but the flight style in this bird was very much more “Common” than “Plain”.
• Size and structure. I have seen a few Plain Swifts in range, and personally wouldn't have any confidence at all in pinning down a lone bird on this. However, there was nothing particularly about the size or structure that made it feel different from Common Swift. I am told Plain does tend to have a longer tail relative to it smaller body size, which I don't think this does. Perhaps more distinctively, the tail tends to be a bit spikier, but in the photos above the tail seems quite normal.

On balance, despite a few folk suggesting otherwise, I would need a fair bit of convincing that this is anything other than a Common Swift, though if I had seen the same bird at a location in which Plain Swift was the default choice, I wouldn't be necessarily be betting my house on this!

Perhaps someone more familiar with the species pair than me will come along and post.

 

[Barred Wobbler]

Plain swift in Tenerife, January 2024, showing tail proportions.