Worth a Thousand Words

This week’s PLoS ONE featured image is taken from a paper published today by Denver Fowler and colleagues at the Museum of the Rockies, Montana State University. In the article, entitled, Predatory Functional Morphology in Raptors: Interdigital Variation in Talon Size Is Related to Prey Restraint and Immobilisation Technique, the authors report that the feet of birds of prey or “raptors” vary considerably among different families in terms of both the curvature of the claws and the claws’ size distribution.

The researchers studied birds from four different raptor families: Accipitridae (hawks, kites and eagles), Falconidae (falcons), Pandionidae (ospreys) and Strigiformes (owls). The featured image shows representative feet from each family: A) and B) represent the Accipitridae family (goshawk and red-tailed hawk, respectively), with enlarged talons on claws I and II; C) peregrine falcon is from the Falconidae family, with small talons and a slightly enlarged claw I; D) great grey owl shows the large talons and relatively little curvature on each digit characteristic of Strigiformes; and E) osprey (from the Pandionidae family) has enlarged, highly recurved talons on each digit.

Fowler and colleagues suggest that the variations in relative size and curvature of the talons across raptor families correlate with the differences in the techniques the birds employ to capture and immobilize their prey. For example, falcons attack their prey at great speed and the impact of this may immobilize the prey in itself. Hawks, eagles and owls, on the other hand, attack their prey on or near the ground and as the prey are less likely to be seriously wounded on capture, these raptors need to be able to restrain their struggling prey. The researchers also propose that the size and shape of the claws varies depending on the size of the prey (defined in terms of whether the prey can be contained entirely within the bird’s foot) and that if the size of the birds’ prey changed, this would necessitate a change in their immobilization strategy.

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