Morphometric Analysis of the Unusual Feeding Morphology of Oriental Honey Buzzards

Abstract

Oriental Honey Buzzards (Pernis ptilorhynchus) are birds of prey that mainly feed on the larvae of social bees and wasps. Previous researchers noted that they have an unusual morphology and it is proposed that this is adaptive to their diet and feeding behaviour. In this study we aimed to quantitatively identify key features of Oriental Honey Buzzards that distinguished them from other birds of prey using morphometric methods. Eighty museum specimens of Japanese raptors (13 Oriental Honey Buzzards, 9 Grey-faced Buzzards, 13 Black Kites, 12 Northern Goshawks, 12 Common Buzzards, 12 Mountain Hawk-eagles and 9 Ospreys) were measured and photographed. PCA analysis, based on 11 head and 11 foot measurements, and landmark based relative warps analysis combined with canonical variates analysis were used to describe morphological variation among the specimens and identify which morphological characters were most important in distinguishing Oriental Honey Buzzards from the other species. We found that the honey-buzzards had a distinctive head morphology, with a long cere and long slit-like nares, and a longer, thinner beak that had a shorter hook at the tip. In relation to their foot size, honey-buzzards had a longer Digit-II and shorter Talon-I and Talon-II than all other species in the study. Long Digits III and IV and shallow tendon depth on the toe were also important in distinguishing Oriental Honey Buzzards from the other species. We suggest that a long, thin beak with a short hooked tip and long digits on the feet are adaptive for extracting larvae from combs and digging wasp nests out of the ground, while the slit-like nares and long cere may offer protection from stings. Identifying key morphological features using morphometric methods allows us to better understand the adaptations and evolutionary processes associated with feeding behaviour in birds of prey.