Post-nestling behaviour in goshawks, Accipiter gentilis: II. Sex differences in sociality and nest-switching

Abstract

Abstract. Relationships between juvenile male and female goshawks, Accipiter gentilis , were studied in 130 fledged broods, in which 187 young hawks were radio-tagged during 1980-1984. The proportion of the smaller male goshawks was least at fledging in broods that had lost most young, possibly because of siblicide by females. Males dispersed at an earlier age than females, especially from large broods and in areas where there were few rabbits; females dispersed early only from broods that hatched late. Distances moved after dispersal were related to rabbit abundance, with males killing fewer rabbits and moving further than females. During the post-fledging period, the spacing of siblings was significantly aggregative in randomization tests. Male fledglings stayed together with other males less than females stayed with other females, but males did not avoid females more than other males, nor did having female siblings accelerate male dispersal. It is therefore suggested that the males dispersed early from poor food areas because they were better developed than females and therefore better able to fend for themselves when food-stressed, and not as a result of being driven away by sisters; their absence would also leave more food for their kin. Eleven early dispensers (10 male, one female) were then recorded for 1-10 days at goshawk nests 2·5-23 km from their own. They switched mainly to nests in the rabbit-rich area, either because only these nests were profitable as a source of food, or because intruders were tolerated only where there was enough food for them not to prejudice the survival of residents.