Age, Arrival Date and Reproductive Success of Male American Redstarts Setophaga ruticilla

Abstract

We tested whether the age-related differences in reproductive success in male Ameri- can Redstarts are caused by differences in date of arrival on the breeding grounds. By relating arrival date to three measures of reproductive success we determined what stage of the breeding cycle is affected by date of arrival. Adult male redstarts were more successful than subadults at obtaining mates. Adult males were also more likely than subadults to have nests built in their territories, and to fledge young. Among mated males, neither age class was significantly more likely to obtain nests. However, among males that nested, there were significant age-related differences in fledging success. Adult males arrived on the breeding grounds before subadults. Within both age classes, males that mated had arrived significantly earlier than those that did not mate. Similarly, males that nested had arrived significantly earlier than those that did not. There were no significant differences in arrival date between males that fledged young and those that did not. Finally, adult males were more likely to renest after nest failure. Therefore, we conclude that reproductive success in male redstarts is independently affected by both arrival date and age, and that the lower success of subadults may not be a consequence solely of their age and late arrival, but also of their lack of experience in selecting territories early in the breeding season.