Causes, consequences and mechanisms of breeding dispersal in the colonial lesser kestrel, Falco naumanni

Abstract

Dispersal is a common phenomenon in animals, with important consequences for individual fitness and the genetics and structure of populations. We studied the causes and consequences of breeding dispersal from an individual perspective using as a model organism the colonial lesser kestrel. For this purpose, we gathered information on 235 birds that attempted to breed in 2 consecutive years (2004–2006) in any of the 22 colonies monitored in the study area. Eighty-two per cent of kestrels returned to the same breeding colony where they had attempted to breed in the previous year. Probability of dispersal decreased with age and individual reproductive performance in the season previous to dispersal and females dispersed more frequently than males. Dispersers settled in colonies with a higher mean reproductive performance than other available colonies located around their colony of origin. However, the size of the colony selected did not differ between selected and surrounding colonies. Thus, dispersers selected highly productive rather than large colonies. Own body condition or the quality of the mates obtained (estimated by their pectoral thickness and size) did not change for individuals that dispersed or for philopatric individuals in subsequent seasons. Although dispersers greatly increased their own breeding performance after dispersal, it did not exceed that of their philopatric counterparts. These results help to explain the coexistence of dispersal and philopatric behaviours within a population and suggest that dispersal may be an adaptive behaviour that increases reproductive performance, particularly for individuals that have suffered a bad breeding experience.