MALE ORNAMENT SIZE AS A RELIABLE CUE TO ENHANCED OFFSPRING VIABILITY IN THE BARN SWALLOW

Many extravagant secondary sexual characters are assumed to have evolv ed as a result of female choice, either because they attract females o r because they reliably reflect the quality of males. Females mating w ith the most ornamented individuals with a superior genotype are expec ted to benefit by producing more viable offspring. A viability advanta ge associated with mate choice can be demonstrated only if (i) parent ornament size reliably reflects parent viability and (ii) offspring vi ability is directly related to the expression of the ornament of the p arent. Barn swallows (Hirundo rustical) are monogamous passerine birds , which are sexually size dimorphic in tail length. Previous experimen ts and observations have shown that females prefer males with the larg est tail ornaments and that male survivors have larger tail ornaments than nonsurvivors. Here I demonstrate that offspring longevity is posi tively related to ornament size of the male parent and that the longev ity of sons is a trait with a statistically significant resemblance to that of their fathers. The viability effects could be entirely due to differences in quality of parental care. However, relative paternal p rovisioning of offspring was negatively related to the tail length of males, while total provisioning rate by both pair members, and thus of fspring body size, body mass, and body condition, was unrelated to mal e tail length. Therefore, females may, through their mate choice, gain an indirect fitness advantage in terms of enhanced offspring viabilit y.