At Lincoln Park Zoo, the local fauna, sparrows, squirrels and rabbits, peacefully co-exist with the gorillas. Not so lucky with the chimpanzees who kill them. We have one chimp who likes to wear dead squirrels on her shoulders like a fur stole.
I saw Grey squirrels in the Gorilla enclosure at Chessington Zoo (UK) the other day- they forage on the food leftovers and travel along the ropes in the enclosure. When the Gorillas are inactive, the squirrels become the main focus of visitor's attention.