Parental defense of offspring and life history of a long-lived raptor

Abstract

Animals with parental care defend their offspring with an intensity reflecting parental investment. Parental investment theory predicts that parents should take risks relative to their residual reproductive value. Therefore, parental defense should change consistently with age reaching a peak at middle age, and it should vary consistently with age at start and end of reproduction. We recorded the intensity of parental defense of offspring in 410 female goshawks Accipiter gentilis throughout their lives, ranging from timid females that barely approached a human intruder at the nest to aggressive females that physically attacked the human. Females were consistent in their level of defense throughout life, and aggressive females were mated to aggressive males. Investment in reproduction as reflected by laying date, clutch size, and brood size showed a bell-shaped relationship with age. Females that started to breed at a young age were less aggressive than females that started late. Likewise, females that finished reproduction at a young age behaved less aggressively than females that finished at an old age. The intensity of defense of offspring peaked at an intermediate age followed by a decrease into old age and senescence. Females that started to breed early during the season were more aggressive than late breeders. These findings are consistent with the hypothesis that the intensity of parental defense of their offspring reflects parental investment and patterns of aging.