Experimental manipulation of tail length in female barn swallows (Hirundo rustica) affects their future reproductive success

Abstract

Previous studies have shown no significant effect of experimental tail length manipulation in female barn swallows (Hirundo rustica) at the beginning of a breeding season on reproductive success or behavior during that breeding season. In the present study, we investigate if tail length manipulation had any effect on reproductive performance the following year, the so-called long-term effect, in contrast to the short-term effects already studied. We found that females with experimentally elongated external tail feathers at the beginning of a breeding season produced less offspring during the breeding season the following year than did females with shortened or unmanipulated tails. These results suggest that tail elongation caused flight deficiencies that deteriorated the condition of females and eventually reduced reproductive success. The finding of long-term effects but no significant short-term effects for female tail elongation suggests that female barn swallows have the ability to adjust immediate parental investment. Detrimental effects of long tails in females in terms of decreased reproductive success might explain why female tails are not as long as those of males. Finally, females mated to long-tailed (sexually attractive) males decreased their reproductive success the following year more than did females mated to short-tailed males, possibly owing to differential parental effort causing a deterioration of their condition.