Reproductive Effort in Long-Lived Birds: Age-Specific Patterns of Condition, Reproduction and Survival in the Wandering Albatross

Abstract

The condition, breeding performance and survival of the wandering albatross Diomedea exulans were studied in relation to the bird's reproductive experience and age. In both sexes, the body weight of immature birds increased steadily with age from 4 to 7 yr. In individual immature females it increased from one season to the next, and only those attaining a threshold value bred, irrespective of their age. At similar ages immature birds tended to be lighter than breeders. The weight of breeding males increased progressively throughout the breeding life, while that of females increased only during the first 15 yr. In contrast to most species the date of laying for first time breeders was earlier than for experienced birds. Experienced birds tended to lay at similar dates from one breeding season to the other. Birds failing to breed during the previous breeding season tended to lay earlier than successful individuals. The size of the egg and breeding success increased with the age and experience of the female to a maximum at 17-20 yr or 5-7 breeding attempts and then decreased in the older or more experienced birds. For first time breeders the breeding success and rate of return was the same for older individuals as for younger. The proportion of birds breeding one year after a failed breeding season was lower in birds breeding for the first time than in more experienced birds. There was no significant difference between the proportion of inexperienced and experienced birds returning to breed two yr after a successful breeding season. Birds with more than eight yr breeding experience also tended to postpone their return after a failed season longer than less experienced birds. Annual survival rate did not vary significantly with age between 4 and 22 yr. Birds older than 27 yr had a significantly lower survival than birds aged 16-22 yr (92.9% compared to 97.2%). This study suggests that in a very long-lived bird like the wandering albatross survival is not influenced by reproduction, particularly in the early ages because the onset of breeding is delayed until the risk of an increased mortality at first breeding has disappeared. Condition has probably an important influence in the decision to breed. The age related changes in breeding performance, condition and survival observed in the wandering albatross are probably influenced by the cumulative effects of an increase in skill and thereafter reproductive restraint at young ages, by the selection of high quality birds at intermediate ages and by senescence at older ages.