Age-dependent breeding performance in Merlins (Falco columbarius)

We examined the effect of age on breeding performance in male and female Me rlins (Falco columbarius) from a natural population using a long-term data set. In the analysis, we examined whether differences in chick hatch date a nd brood size associated with parents of different ages arose due to select ion of superior individuals (differential mortality hypothesis) or to chang es within individuals over time (inadequate experience hypothesis). In addi tion, we examined the effect of longevity on production of recruits and lif etime reproductive success (LRS). In both sexes, breeding performance impro ved with age. In females, this was mainly the result of disproportionate mo rtality of inferior breeders, with less evidence to support performance cha nges within individuals. Among males, changes in breeding performance with age were largely the result of improvements within individuals early in the ir life (between age 1 and 2+). Production of recruits was not dependent on parental age at the time of breeding for either sex. Recruit production an d LRS were both influenced by longevity. so that longer-lived birds produce d more offspring over their lifetimes and thereby had a greater probability of producing recruits. The differences between the sexes in terms of age-d ependent breeding performance are likely a consequence of the differing rol es the two parents play in reproduction. Male Merlins provide most of the f ood for the pair and their young during the breeding season, and changes in hunting skill with age may account for individual improvements in breeding performance.