Abstract
Despite the ubiquity of raptors in terrestrial ecosystems, many aspects of their predatory behaviour remain poorly understood. Surprisingly little is known about the morphology of raptor talons and how they are employed during feeding behaviour. Talon size variation among digits can be used to distinguish families of raptors and is related to different techniques of prey restraint and immobilisation. The hypertrophied talons on digits (D) I and II in Accipitridae have evolved primarily to restrain large struggling prey while they are immobilised by dismemberment. Falconidae have only modest talons on each digit and only slightly enlarged D-I and II. For immobilisation, Falconini rely more strongly on strike impact and breaking the necks of their prey, having evolved a ‘tooth’ on the beak to aid in doing so. Pandionidae have enlarged, highly recurved talons on each digit, an adaptation for piscivory, convergently seen to a lesser extent in fishing eagles. Strigiformes bear enlarged talons with comparatively low curvature on each digit, part of a suite of adaptations to increase constriction efficiency by maximising grip strength, indicative of specialisation on small prey. Restraint and immobilisation strategy change as prey increase in size. Small prey are restrained by containment within the foot and immobilised by constriction and beak attacks. Large prey are restrained by pinning under the bodyweight of the raptor, maintaining grip with the talons, and immobilised by dismemberment (Accipitridae), or severing the spinal cord (Falconini). Within all raptors, physical attributes of the feet trade off against each other to attain great strength, but it is the variable means by which this is achieved that distinguishes them ecologically. Our findings show that interdigital talon morphology varies consistently among raptor families, and that this is directly correlative with variation in their typical prey capture and restraint strategy.
Highlights
Birds of prey or ‘‘raptors’’ (Accipitridae: hawks, kites, and eagles; Falconidae; Pandionidae: the osprey; and Strigiformes: owls) are among the most familiar and geographically widespread of all vertebrates
Our method is preferable to those of previous workers as it encompasses a full range of measurements, treating the foot as a whole, and because previously published qualitative accounts of predatory behaviour did not consider the influence of variation in talon morphology, necessitating reinterpretation which we present here
Given that other variable elements of the foot perform clear functional roles [16,17,19], and that there is correlation between claw morphology and function in terrestrial through arboreal birds [25,34], it is likely that raptor talon morphology does vary dependent on function, since raptor feet are so important for prey capture and manipulation
Summary
Birds of prey or ‘‘raptors’’ (Accipitridae: hawks, kites, and eagles; Falconidae; Pandionidae: the osprey; and Strigiformes: owls) are among the most familiar and geographically widespread of all vertebrates. They are admired for their predatory ability, but surprisingly little is known about the patterns of physical interaction between predator and prey during capture and dispatch. It has often been assumed that raptors mainly use their sharp talons (a specific term referring only to the claws of birds of prey) to kill their prey [1] This misconception is rooted in the difficulty of tracking and observing aerial predators after a prey item has been captured [2,3,4,5]. The term ‘‘immobilisation’’ (where the victim is no longer capable of movement or retaliation) is preferred to ‘‘killing’’ because in some accipitrids at least, if the prey is suitably immobilised and subdued, the raptor will commence feeding even before the death of its victim [6,7,8]
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