Hierarchical dominance structure in reintroduced California condors: correlates, consequences, and dynamics

Abstract

Populations of reintroduced California condors (Gymnogyps californianus) develop complex social struc- tures and dynamics to maintain stable group cohesion, and birds that do not successfully integrate into group hierar- chies have highly impaired survivability. Consequently, im- proved understanding of condor socioecology is needed to inform conservation management strategies. We report on the dominance structure of free-ranging condors and identi- fy the causes and consequences of rank in condor populations by matching social status with the behavioral and physical correlates of individual birds. We characterized the hierarchical social structure of wild condor populations as mildly linear, despotic, and dynamic. Condor social groups were not egalitarian and dominance hierarchies reg- ulated competitive access to food resources. Absence of kin- based social groups also indicated that condor social structure is individualistic. Agonistic interactions among condors were strongly unidirectional, but the overall linearity and steepness of their hierarchies was low. Although one aggressive male maintained the highest dominance rank across the 3-year observation period, there was considerable fluidity in social status among condors within middle and lower rank orders. Older condors were more dominant than younger birds and younger males supplanted older females over time to achieve higher status. Dominance rank did not predict the amount of time that a bird spent feeding at a carcass or the frequency that a bird was interrupted while feeding. Thus, younger, less dominant birds are able to obtain sufficient nutrition in wild social populations.