The function of long tails in female barn swallows (Hirundo rustica): an experimental study

The outermost tail feathers in male barn swallows (Hirundo rustica)are the target of a strong directional female mate preference.The tail ornament is also expressed in females, since femaleshave considerably longer tails than juveniles, either due to(1) a strong genetic correlation between the characters in thetwo sexes, or (2) direct sexual selection on females. To discriminatebetween these two hypotheses, we manipulated the length of theoutermost tail feathers in female barn swallows shortly afterarrival by either shortening or elongating the outermost tailfeathers, or maintaining their length among control individuals.Start of laying of the first clutch, reproductive performance,or provisioning of offspring did not show any significant differencesamong treatments. Original female tail length before manipulationwas unrelated to reproductive performance, while male tail lengthexplained some variation in the number of clutches and, to someextent, the total number of eggs laid per year. Females withlonger tails arrived earlier at the breeding grounds. Manipulatedfemale tail length was positively correlated to the tail lengthof their mates. Our results support the correlated responsehypothesis but do not support the sexual selection explanationfor the existence of exaggerated tail feathers in female barnswallows.