Segregation in the African wintering ranges of English and Swiss Swallow Hirundo rustica populations:: a stable isotope study

Capsule Stable isotope analysis of Swallow feathers, grown in Africa, revealed significant differences between populations breeding in Switzerland and England. Aims To investigate the extent to which Swallow populations breeding in Switzerland and England are separated on their African wintering grounds. Methods Swallows were caught at breeding colonies, biometric measurements were taken and feathers, grown in Africa, were collected. Feathers were combusted in a Carlo Erba C/N/S analyser and the delta(13)C and delta(15)N signatures were measured using a mass spectrometer. Results The delta(13)C signatures of Swiss birds were significantly more depleted than those of birds from England. The delta(15)N signatures did not differ between the two populations. Conclusion Birds from Switzerland and England probably winter in geographically distinct parts of Africa. The Swiss birds probably feed on prey that are more reliant on C-3 vegetation, from woodlands, than the prey of English birds, which are more reliant on C-4 vegetation, from grasslands.