Richard...most of the time Peregrines kill in the air. Most often they close their talons making a fist and in their dive,which can be over 300kmh they slam the prey and grab it before it hits the ground. Smaller prey are dead on contact,if no then,finished when grabbed. Often in flight U can see them rip the head of the prey off. Some prey has its back broken in the strike and is finished off when grabbed. The one talon sort or rips/cuts the head off,or right into the neck and severes the spinal chord,leaving them feeling nothing. Its all over very fast. Often a puff of feathers is all you see..its over by then. I have seen them take half live pigeons to young ones to sort of show them how to finish it off. One year at Etobicoke at Islington and Bloor,the 2 adults in succession struck a Turkey Vulture. Its back was broken it folded its wings and plummeted to its death. I have seen them cherry pick too....at the Liftbridge they will go into the steel girders of the bridge,where pigeons nest and just take squabs out. They also do this under the Skyway Bridge. Ive also seen Peregrines panic flight the pigeons and chase one. The pigeon in a panic slams into an apartment balcony and the Peregrine catches the bird on the rebound,already dead from the impact. Short answer it can be either way...dead on impact or finished off quickly. Either way its very fast!
