Symmetrical male sexual ornaments, paternal care, and offspring quality

Abstract

Simultaneous manipulation of tail length and tail asymmetry in male barn swallows (Hirundo rustica) has revealed that females prefer maJes with both long and symmetrical tail ornaments over males with short and asymmetrical ornaments. Fluctuating asymmetry in tail length has a negative effect on the maneuvering ability of male barn swallows, and females may prefer males with symmetrical tail ornaments because they thereby acquire more direct fitness benefits in terms of paternal care. The least preferred males with short tails with high asymmetry performed an absolutely and relatively larger share of feeding of nestlings than the most preferred males. However, the combined feeding rate of the pair was not statistically significantly different between treatment groups. Fully grown tarsus length and body mass of offspring on day 15 did not differ between treatments. These results indicate that females do not prefer males with symmetrical tail ornaments because such males contribute a relatively or absolutely larger share of parental duties. Although these results do not explain the basis of female choice for long and symmetrical tails, the results are consistent with a hypothesis that females of species with biparental care should invest differentially in their offspring relative to the quality of their mates. The results are also consistent with a hypothesis that preferred males have access to mates with superior parenting abilities