I found this guy about 50' from the nest on the grass.

My guess is that he/she fell out of the nest and was flittering around and a dog off leash got to him. There are a lot of people who bring their dogs to walk them in this park, many who are basically clueless idiots and let their dogs run around off their leashes. The reason I am guessing dog here is that most of the bird is untouched. If it were a wild animal, there would be feathers only, perhaps a foot or two, they'd eat the bird. A dog wouldn't care and if the owner actually noticed what their pet was doing, they'd probably pulled the dog away and left the scene quickly.