Barn Swallow Hirundo rustica transitiva and H. r. erythrogaster, 'American Barn Swallow'
Birds resembling transitiva, from southeast Europe, and erythrogaster, from North America, have been suspected in Britain. It seems that transitiva differs from British rustica only in the intensity of colour on the underparts. The vagrancy potential of the former is obscured by the not-infrequent presence of transitiva-like individuals during spring migration in Britain, which appear to be variants within the west European population. Consequently, on current knowledge, a ringing recovery or molecular data would be needed to prove the occurrence of transitiva.
The North American erythrogaster is rather distinctive and consistent in appearance. Differences relate to the head and underparts, with erythrogaster lacking the dark band below the chestnut throat. Although rustica may (rarely) resemble erythrogaster – e.g some juvenile rustica may show a weaker, broken breast-band – such resemblances are superficial, and carefully observed erythrogaster should be identifiable in a majority of cases. Claims should be supported by detailed notes and, ideally, images and we welcome photographs of unusual-looking birds for our files. (Turner & Rose 1989; Sibley 2000; Jiguet & Zucca 2005)
