ASPECTS OF THE HINDLIMB MORPHOLOGY OF SOME AUSTRALIAN BIRDS OF PREY: A COMPARATIVE AND QUANTITATIVE STUDY

Abstract

We quantified the extent of adaptive radiation in the evolution of the hindlimb in the bird-of-prey community on Tasmania. Assessments of the ecological capabilities of raptor species are often based on a visual inspection of their hindlimb structure, with little recourse to direct biomechanical or functional evidence. We examined the links between hindlimb structure and patterns of diet, foraging, and habitat use in raptors by analytically investigating tarsus, toe, and talon measurements. We identified groupings on the basis of dietary preference, hunting-killing technique, and phylogeny. We found that the bird-catching specialists, which possessed relatively long digits with short talons, were consistently separable. The large-mammal and fish specialists were equipped with relatively short and robust tarsi, and short digits with long and robust talons. The hindlimbs of medium-mammal specialists were characterized by long digits and a large digit 1 talon. However, the generalist group did not possess any specializations, because their structural elements were comparable to those of other dietary groups. An association was found between the ratio of toe to talon length and the selective pressures of prey capture and ease of killing. Morphological variation in this feature was consistent with phylogeny, because the Accipitridae were characterized by a larger ratio of toe to talon length on digits 1 and 2 than the Falconidae, and the diurnal raptors possessed an interdigital pattern of larger variation in ratio of toe to talon length than the nocturnal raptors. No link was found between dietary habit and tarsus length or robustness, because these features were apparently attributed to variations in hunting style. Our analysis highlights the interrelationship between the morphology of hindlimb structure and the functional pressures associated with predatory lifestyles. Aspects de la morphologie des membres postérieurs de quelques oiseaux de proie australiens : Une étude comparative et quantitative