|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.|
|The thick blue breast band and dark rufous face rule out the North American form erythrogaster, which also typically shows strongly rufous-washed underparts.|
|The same bird in flight, showing that the rufous washing extends fully over the underparts and underwing coverts.|
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.