FUNCTIONAL MORPHOLOGY OF RAPTOR HINDLIMBS: IMPLICATIONS FOR RESOURCE PARTITIONING

Prey capture in owls and hawks is largely dependent on the biomechanics of the hindlimbs, and both limb size and grip forces potentially determine the size of prey that can be captured and the extent of possible resource partitioning among sympatric species. Morphological study of six species of sympatric raptors—the owls Otus asio, Strix varia, and Bubo virginianus; and the hawks commonly considered their diurnal “ecological equivalents,” Falco sparverius, Buteo lineatus, and Buteo jamaicensis—revealed that, in both groups, talon closure is effected by two discrete mechanisms that function together in a potentially additive or alternative fashion. Grip force measurements obtained from live owls and hawks using “hydraulic” perches showed that grip force increases exponentially with body size and that owls produce greater forces than hawks. That finding is consistent with the distinctive osteology and myology of their hindlimbs and with their hunting behavior. These data provide some understanding of the different demands of diurnal and nocturnal hunting as well as the mechanism of coexistence for those six species in eastern woodlands.