Blog Pick of the Month – November 2009
It’s that time again, the first of the month and the time to announce the Pick Of The Month award for November.
There were 18 blog posts covering PLoS ONE articles aggregated on ResearchBlogging.org in November. And the one that caught my attention was How Raptor Talons Fit Their Prey by John Beetham from the DC Birding Blog. John writes:
The first thing to understand is that raptors do not usually kill their prey by wounding them with their talons or beaks. Instead, most raptors kill their prey by constriction – squeezing their prey so tightly that death comes by asphyxiation. In a minority of cases, this squeezing motion may cause fatal injury if a talon pierces a vital organ. In other cases, a raptor may start dismembering and eating its prey before the prey is fully dead.
Given the prominent role that a raptor’s feet play in seizing prey, it makes sense that the shape of their feet might vary with how a raptor uses them. This is in fact the result reached by a team of graduate students after they photographed and measured the feet of hundreds of bird specimens, both raptors and non-raptors.
The post describes, and puts into context for avid birders, the PLoS ONE article Predatory Functional Morphology in Raptors: Interdigital Variation in Talon Size Is Related to Prey Restraint and Immobilisation Technique by Denver W. Fowler, Elizabeth A. Freedman and John B. Scannella of Museum of the Rockies, Montana State University:
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.
Congratulations both to John Beetham and to the authors of the article. I have notified the winners and their prizes are on the way. I hope you read John’s post and post a comment of your own, and then go to the article itself to read it and post comments, notes and ratings there as well.