Philippine birds of prey: Interrelations among habitat, morphology, and behavior

Abstract

We sought to clarify relationships among morphometrics, behavior, and ecological variables for 21 species of raptors in the Philippines. Morphological space was de- fined by 42 external characters analyzed as shape variables with respect to body length (without tail). Seventeen variables were used to characterize habitat and five to characterize foraging behavior. Three PCA components accounted for 68% of the total variance in the habitat data and separated species living in dense forests from those using degraded habitats or coastal areas. Two PCA components explained 81% of the variance in hunting mode, with transitions from sit-and-wait to flap-gliding, and with contrasts between soaring and flap- gliding. Three PCA components accounted for 70.5% of the variance in morphological shape. The first component separated species with narrow wings and less-pronounced notches from species with broad, deeply notched wings. The second and third components were associated with the contrast between pointed and rounded wings and prey-capture apparatus (feet, bill). Five morphological characters were highly correlated (R = 0.934) with the first principal component of the habitat data, indicating that species inhabiting forested habitats have square tails, rounded wings, and strong claws. Hunting mode and habitat also were closely related (R = 0.900). Soaring correlated well with the number of notched primaries, tail shape, and measures of the trophic apparatus, but poorly with wing loading and aspect ratio. Behavior, ecology, and morphology of this subset of raptors were closely interrelated. Among the Philippine raptors, species that inhabit rain forests are the most endangered, and we suggest that morphological constraints limit their use of secondary habitats.