http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0007999
Predatory Functional Morphology in Raptors: Interdigital Variation in
Talon Size Is Related to Prey Restraint and Immobilisation Technique
Denver W. Fowler*, Elizabeth A. Freedman, John B. Scannella
PLoS ONE 4(11): e7999. doi:10.1371/journal.pone.0007999
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.
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