AGE-DEPENDENT BREEDING PERFORMANCE IN MERLINS(<i>FALCO COLUMBARIUS</i>)

Abstract

We examined the effect of age on breeding performance in male and female Merlins (Falco columbarius) from a natural population using a long-term data set. In the analysis, we examined whether differences in chick hatch date and brood size associated with parents of different ages arose due to selection of superior individuals (differential mortality hypothesis) or to changes within individuals over time (inadequate experience hypothesis). In addition, we examined the effect of longevity on production of recruits and lifetime reproductive success (LRS). In both sexes, breeding performance improved with age. In females, this was mainly the result of disproportionate mortality of inferior breeders, with less evidence to support performance changes within individuals. Among males, changes in breeding performance with age were largely the result of improvements within individuals early in their 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 and LRS were both influenced by longevity, so that longer-lived birds produced more offspring over their lifetimes and thereby had a greater probability of producing recruits. The differences between the sexes in terms of age-dependent breeding performance are likely a consequence of the differing roles the two parents play in reproduction. Male Merlins provide most of the food 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.