Most birders learn through field guides that different raptor groups have recognizable body shapes adapted to the way they hunt. Accipiters, for example, have short rounded wings and long tails to facilitate short pursuits through close quarters. This is, in fact, a key to identifying many raptors in the field. Close study of raptors reveals even more subtle anatomical differences. A newly published article in PLoS ONE relates differences in the shapes of raptor talons to how they kill their prey.
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. (Most specimens were held by Montana State University; others were from the American Museum of Natural History.) The most significant differences in claw shape were among raptor families and distinguished raptors from non-raptors.
Here are the significant characteristics of each raptor family:
- Accipitridae (including accipiters, buteos, and eagles) have first and second talons (D-I and D-II) that are exceptionally large in proportion to their other talons.
- Falconidae have talons that are more equal in size than Accipitridae but D-I and D-II continue to be proportionately larger.
- Strigiformes have large talons that are more equal in size mounted on short strong toes.
- Pandionidae have long and exceptionally curved talons. The largest talon, D-IV, can rotate so that an osprey can grip its prey with two talons on one side and two on the other.
Fowler, D., Freedman, E., & Scannella, J. (2009). Predatory Functional Morphology in Raptors: Interdigital Variation in Talon Size Is Related to Prey Restraint and Immobilisation Technique PLoS ONE, 4 (11) DOI: 10.1371/journal.pone.0007999