The Dr. Dolittle stories are fantasy, not nature lore. It is important that the animals are animals, but the stories are the stories of interesting adults. They have strengths and weaknesses. They are characters with intention, not simply buffeted by fate. Nor do they exist to testify about humans.
Some animal stories are thinly disguised stories about people, and to hell with nature lore.
Among other motivations to write animal stories are two having to do specifically with animals as epitomes of the voiceless, the helpless and the innocent. And sometimes the author wishes to make the innocent speak up for the author and the author's friends, to act as character witnesses whose own characters are unimpeachable. That's what John Berger and Paul Auster are up to with their dog books. In general, animals aside, no one needs advocates more than those who are innocent, helpless and voiceless, three attributes that are often found together. These are also traits of an attractive constituency.