The gorilla is an older female named Samantha. She was the last of her troop at the zoo. At her age, it was felt that she was unlikely to integrate into a new troop.

The zookeepers did not want her to be lonely, so they introduced a rabbit named Panda into the exhibit much as they would introduce a new animal. The rabbit began behind a screen, progressed to a large mesh box and eventually to being in the exhibit. He had a safe area that he could access at any time, but, as the photo shows, it was not really needed. It did help him feel safe, though.

It has been two-and-a-half years, so I do not know what the status of the pair is, but she was definitely doting on this little guy while I was there.

There was a very brief article on Huffington Post on the two.
http://www.huffingtonpost.com/2012/03/09/samantha-erie-zoo-gorilla-bunny_n_1335513.html