Parry, Steven James; (2001) The booted eagles (Aves: Accipitridae): Perspectives in evolutionary biology. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The monophyly of the booted eagles (genera Ictinaetus, Aquila, Hieraaetus, Polemaetus, Spizastur, Lophaetus, Spizaetus, Stephanoaetus and Oroaetus) has been accepted for over a century. This study critically appraises the taxonomy, systematics, autecology and morphology of the 33 recognised species of booted eagle. Evidence is presented which demonstrates that two currently recognised subspecies (Aquila pomarina hastata and Hieraaetus morphnoides weiskei) should be treated as valid biological species. It is also argued that Aquila adalberti should be treated as a subspecies of Aquila heliaca. Body mass distributions in the booted eagles are compared with those in other accipitrid clades and interpreted ecologically. By reference to biomolecular phylogenies phyletic size increase is demonstrated and interpreted in terms of ecology and flight adaptation. Integumental and osteological morphology are investigated via body mass allometry and multivariate analyses. Interspecific differences and similarities in morphological adaptation are interpreted with respect to predation and flight strategies. The ontogenetic basis of accipitrid phenotypic evolution is also investigated. Flight performance analyses are presented and a body of general theory concerning flight adaptation in accipitrid raptors is developed. The dichotomy between soaring and flapping flight is emphasized and its implications for migration, dispersal and island colonisation discussed. Rectricial dimensions in the booted eagles are interpreted with respect to aerodynamic theory, sexual selection and handicap theory. The potential of ecomorphological analysis as a predictive ecological method is demonstrated by reference to Aquila gurneyi and Spizastur melanoleucus. Indices of sexual dimorphism are calculated and interpreted with respect to the conflicting theories concerning its evolution in accipitrid raptors. Discriminant analyses are presented for sexing all principal booted eagle taxa via external biometrics. Whilst several factors may contribute to the evolution of reversed sexual dimorphism, the degree of dimorphism is interpreted as being due to intersexual niche partitioning and sexual selection. It is concluded that although the booted eagles are morphologically conservative they are probably polyphyletic, constituting a grade rather than a clade.

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