The role of intrinsic factors for the recruitment process in long-lived birds

Abstract

Recruitment to the breeding population is one of the most important and complex steps in the life history of long-lived animals, with great consequences for their reproductive career. Longitudinal data on individuals has provided new information on recruitment to the natal colony. We approach recruitment from the individual level, and address intrinsic factors affecting the probability of recruitment. Key steps to recruitment to the natal colony are fledging, subadult survival, the return to the natal area, the decision to breed there, and the ability to do so. Determinants characterising the state of an individual before recruitment can have a genetic basis (such as sex, mass) or can originate from the individual’s experience (e.g. degree of parental care, number of siblings and rearing conditions affecting mass and age at fledging—or length of the subadult period). Recruitment depends also on age, experience and body condition, increasing with the number of prospecting years spent at the colony. Threshold levels in body mass and arrival in due time are preconditions to successful first breeding. The improvement of body condition with age may be mainly due to an increase in foraging efficiency, increasing the resources which can be allocated to reproduction beyond those needed for self-maintenance. Prospecting and attendance leads to the acquisition of skills favouring recruitment, concerned with establishing a territory, mating, courtship and chick feeding. It is suggested that the individual optimal age of recruitment is produced by balancing the risk of premature breeding, with the consequent reduction in survival, against the advantage of presumed increased breeding opportunities with the concomitant increase in lifetime reproductive success.