NATAL DISPERSAL AND DEFERRED BREEDING IN THE BLUE-FOOTED BOOBY

Abstract

Male Blue-footed Boobies (Sula nebouxii) first nested at an age of two to six years = 4.7), and females a little earlier at one to six years (x = 3.6). Both sexes nested selectively close to the natal site in their first reproduction (males 24.1 m, females 28.3 m) and similarly close to the natal site in their second reproduction, despite displacement from first to second site. First sites of both sexes were similarly close to the natal site and the parents' current site, and parents dispersed only 26.2 m between hatching and first reproduction of their offspring. Throughout their lives, both sexes may tend to nest close to the natal site and, hence, close to kin. Nonetheless, given high nest density in the colony (0.0356 nests/iM2) and high variance in natal dispersal (males, SD = 33.1 m; females, SD = 35.2 m), inbreeding and social interactions with kin are unlikely to result. Overall, these results do not support the hypothesis that philopatry in some marine birds and other animals functions to achieve an optimal balance between inbreeding and outbreeding. Received 3 October 1991, accepted 28 May 1992. THE DISTANCE moved by a bird from the nest site where it hatched to the nest site of its own first reproduction (natal dispersal) may have an important influence on gene flow between and within populations, and on the evolution of social behavior (e.g. Mayr 1963, Greenwood et al. 1979a). Limited dispersal (philopatry) is com- mon in birds and, in most species, females dis- perse farther than males (Greenwood et al. 1978,