Intersexual differences in age-specific parental effort in the house finch (Carpodacus mexicanus)

Although age-specific improvements in reproductive performance are common in iteroparous organisms, they are by no means universal. Reproductive tradeoffs are integral features of the life-histories of animal populations and may lead to complex breeding strategies among birds of different age. In particular, asymmetries in the costs and benefits of different components of reproduction for males and females may result in contrasting patterns of age-related parental investment between the sexes. We examined age-specific patterns of parental care in an eastern North American population of house finches (Carpodacus mexicanus) over a three-year period and found pronounced differences in the degree to which males and females provisioned young as they aged. Younger male house finches provided more care to offspring than did older males, yet in females it was the middle-aged mothers that provisioned young most often. This pattern of paternal care is inconsistent with condition- and experience-dependent investment, and instead may reflect male compensation for decreased maternal performance or an attempt by males to secure future breeding attempts with their mate. In contrast, the pattern of maternal provisioning mimics age-related trends in other female breeding efforts (e.g. clutch size, fledging success) for short-lived passerines, which may be governed by condition, experience, and the onset of senescence. These data emphasize the variability in parental tactics that characterizes birds of different sex and age, and the importance of considering the allocation of reproductive effort to competitions for mates, egg-production, and parental care in relation to age so that we may better understand the evolution of male and female breeding strategies in birds.