We are feeding two or three (Not sure if it is a male and one or two females) in our garden since October, and have noticed that all of them have limped at one time or another.
Our security videos show that they prefer to jump onto and off obstacles rather than walk around them so I wonder if they get an occasional awkward landing and a sprain. None of ours have a permanent limp.
Their preferred food is an egg and Sainsbury's own adult dog food.