A lot of linguists refuse to acknowledge that animals other than humans can use language. In my opinion, it's because of the way they define language; specifically, as nothing other than fully formed syntactical language. So if that's the definition, then fine, it's only humans. If the definition is expanded AT ALL, you have to accept that other species use language.

Then there's the question of intelligence. Again, many scientists refuse to acknowledge that other species are intelligent for a whole host of reasons.

This video from Ted.com shatters both of these notions. Clearly, Bonobos are both capable of using language and remarkably intelligent. 

Peace and Love and Empathy,

Matt