What are the use of raptorial feet?

This blog will focus heavily on families that hunt their prey such as Accipitridae, Falconidae, Strigiformes and Pandionidae: osprey. 
Beside their eyes, these raptors also have their feet that make them lethal hunters (Fowler, Freedman & Scannella 2009). Although while you might find that these raptors all have the characteristic feet, the talons and digit positioning between species have subtle but significant differences (Fowler, Freedman & Scannella 2009). But despite these differences all raptorial feet share a common function; that is to capture, restrain and immobilise their prey (Fowler, Freedman & Scannella 2009).

Accipitridae is distinguishable by their enlarged talons on the I and II digits, Falconidae by the elongated III digit, Strigiformes by their large but not very rounded talons and Pandionidae from the large equal sized, largely rounded talons found on all digits (Fig1.) (Fowler, Freedman & Scannella 2009). These differences are due to prey preference and the way in which these raptors capture and immobilise their prey (Fowler, Freedman & Scannella 2009). The enlarged talons on Accipitridae are thought to restraining larger prey items, where death occurs through being eaten alive causing blood loss and organ failure (Fowler, Freedman & Scannella 2009). Falcons on the other hand like the peregrine falcon predate birds, flying at high velocities in order to dislocate the spine but when this isn’t effective they’ll overpower the bird and sever the spine with their beak (Fowler, Freedman & Scannella 2009, Brown  & Amadon 1968). In contrast, owls will tend to prey primarily on smaller rodents, thought to be why owls have less curve to their talons and have the specific positioning of their digits, that they might be able to entirely grasp prey rather pierce their prey (Fowler, Freedman & Scannella 2009).  Finally, osprey unlike birds and rodent hunting raptors hunt fish, where their feet have sharp spicules for enhanced grip in addition to their largely curved talons restraining and immobilising their prey items (Brown  & Amadon 1968, Fowler, Freedman & Scannella 2009, Poole, A.F., 1994).

Fig1. Feet of Accipitridae (A, B), Falconidae (C), Strigiformes (D) and Pandionidae (E) with labelled digits I, II, III, IV (by Fowler, Freedman & Scannella 2009). 

References: 

Brown, L. & Amadon, D. 1968, Eagles, hawks and falcons of the world, Country Life Books, Feltham, pp. 17-29.

Fowler, D.W., Freedman, E.A. & Scannella, J.B. 2009, "Predatory functional morphology in raptors: Interdigital variation in talon size is related to prey restraint and immobilisation technique", Plos One, vol. 4, no. 11, pp. e7999.

Poole, A.F., 1994, “Family Pandionidae (Osprey)”, Handbook of the birds of the world, vol. 2, pp.42-50.