Critters are most active in the early morning or late evening. It's as if they have no respect for photographers who want to photograph them. Seriously, the nerve of these animals.... Anyway, in order to photograph them when they are active you have to shoot in some pretty low light situations. Here you will find some suggestions on how to make the best of what nature provides you.
The Nikon 80-400mm f4.5-5.6 AF-S is supposed to be an update of their older model. However, this lens is much more than an update. It is seemingly a full redesign on the inside with only minor tweaks to the outside. If you are looking for a reasonably priced telephoto lens that will allow you to reach 400mm then this is the way to go.