Emily,
long lenses are great if you have the room to use them. My studio shots have 15 feet between me and the subject. A 300 mm isn't going to work under those conditions. Same in most houses when I go on location.

For outdoor shooting, I use the 70-200 zoom and I do like the compression you get at the longer settings but I don't like working that far away from my subjects since I interact with them a lot. It's a matter of how you work with the animals I guess. I get their trust and then talk to them. It seems to work in the majority of cases.

Jim