I read this series when I was very young so the details are fuzzy, but I remember it being about a race of animals resembling rodents or monkeys with no normal speech or anything. However, they have a highly organized sort of tribal society.
I can't remember exactly how many books there were, but I think there were at least four or five. The first few books were adventures set on the alien planet, which was pretty idyllic and beautiful. I remember the aliens moved through the branches of trees.
Throughout the series, the planet was colonized by humans who didn't realize the alien creatures were sentient. The humans proceeded to just move in, assuming there was no preexisting society. The story followed some of the animals/aliens as they struggled in a new human society that saw them as animals.
I vaguely remember scenes where the creatures were kept in cages like gerbils and fed a special food. I think there may have been an animal experimentation scene in it as well.
At the end of the series, some of the aliens finally get the hang of human communication and manage to convey that they're sentient. I feel like there may have been books after that but I'm not sure.
If anyone knows this series, I would really appreciate the help! The memory of these books gets really stuck in my head sometimes and I'd love to re-read them as an adult!