Tail length correlates with fat stores in pre-migratory roosting Barn Swallows Hirundo rustica

Elongated outer tail streamers in Barn Swallows may play a functional role during the feeding activity, by enhancing manoeuvrability. Here we focus on the relationship between tail length and fat stores in adult male and female Barn Swallows captured during the post-breeding and pre-migratory periods. Fat score was higher among long-tailed males, but no such relationship was evident among females. However, the effect of tail on fat stores did not differ between the sexes. Hence, the relationship between fat and tail may be related both to naturally and sexually selected aspects of tail length, that is considered to be a sexually selected character and indicator of individual quality in males. Our results suggest that long-tailed males, due to their higher quality, may be able to raise their fat stores more than other individuals during the pre-migratory fattening period, and, at the same time, that long-tailed individuals of both sexes may be able to store food faster, according to the aeroelastic properties of outer tail streamers.