Not sure if Gorillas qualify for portrait consideration, but I would at least ask to be given a chance with readers. Poor guy is spending his life in a cage for our experience, allow him to express himself for a moment to OP's readers.
I loved the expression of this caged fellow At the Washington D.C. National Zoo. However, it was a very difficult shot technically because I had a sort zoom range only about 112mm(35equiv.),it was dark, and I had to shoot through appx. 1" thick dirty glass. But I just had to try. He patiently held his pose and gaze till I got it. Felt bad he was living in his head, but at least he seemed to have happy thoughts.