Competition and patterns of resource use by two sympatric raptors

We examined the diets of two sympatric raptors, Swainson's Hawks (Buteo Swainsoni) and Harris' Hawks (Parabuteo unicinctus), during a prey decline that resulted in lowered reproductive success for both species. Contrary to the predictions of competition theory, diets of the two species did not become more specialized. However, we observed interspecific aggression by Swainson's Hawks, which evidently defended a large territory against Harris' Hawks. We conclude that direct competition for food did not take place between these two hawks because such competition was mediated by competition for territories and the subsequent partitioning of space.