The interests of the sexes are not always coincident, and parents may not agree for at least two reasons on how to distribute parental care. Relatedness between offspring and parents, and offspring sex may affect the relative contributions of male and female care givers, as well as how they invest in sons and daughters. This study addresses the effects of parentage and offspring sex on parental provisioning in Mountain Bluebirds (Scialia currucoides). Preliminary results suggest that Mountain Bluebird males but not females bias their feedings toward male-biased broods. In addition, male care givers appear to feed less, on average, than female care givers do, suggesting that male certainty of parentage is lower than that of females. Patterns of allocation of parental care will be determined by 1) observations in the field, 2) video-taping of activities in the nest, 3) manipulation of number of males and females in the nest (sex-ratio), 4) manipulation of proximate factors, such as nestling postion. Parentage will be assigned using DNA fingerprinting. Mountain Bluebirds are particularly instructive in terms of the evolution of parental care because this species is a member of a clade (the genus Siala) in which the other two members show opposite trends in sex-biased provisioning of offspring.
