I dislike zoo pictures myself, just because it feels like you're shooting fish in a barrel (only with a camera instead of a gun) . That being said...
1. The first shot has a cuteness to it. I went "awwww... cute." Literally.
2. Several of the shots (notably first and last) are soft- looks like you may have missed the focus. A bit of a sharpening pass will improve it some.
3. When doing zoo shots, try to do your best to minimize any obviously man-made or man-placed objects (fences, burlap sacks, Xbox 360s, etc.)