You might want to try www.orangutan.org. One of their papers describes attempts to teach orangutans Ameslan and compares it with other ape linguistic experiments.

Orangutans appear to be less adept at learning Ameslan than do chimpanzees or gorillas. This may be because orangutan intelligence is more spatial-mechanical and less social-verbal than that of other apes; it may also be that the Broca's area had already evolved to some extent in the common ancestor of gorillas and bonobos-chimps-humans, and that this evolution occurred largely _after_ the orangs split off from that line.