When I was a child in the 1970's, there was a one legged Mockingbird and a blackbird that would come to the backyard, and the blackbird would sit on the fence and screech until the Mockingbird would bring it food (worms, etc). My mother and I would watch the two, trying to figure out what caused this behavior. The two of them came around for about 2 or 3 years, and we would put out food for them. The blackbird would not feed itself, the mockingbird always put the food into the blackbirds beak, as if it was its child. The fact the Mockingbird had only one leg and was nearly 5 times smaller than the blackbird was puzzling as well.