Well, there's a first I did not know, Cattle Egrets eat mice. Do tell!
Egrets, storks and herons will eat anything that moves and they can fit in their mouths. They are the least discriminationg of any predator I can think of. They eat other birds, reptiles, amphibians, mammals, insects, you name it and they will eat it. Google images for "heron eating" it's pretty amazing and the egrets aren't much more pickey.