Most wildlife photographers agree that to even start out photographing birds in the wild you need at least a 600mm lens. I'm not sure I agree. The following images where created with a 70-200mm zoom. Granted I had to get close but with some patients its quite possible to get good results with out lugging around a small Hubble telescope.
Canon EOS XTi
Canon EF 70-200mm f/4L IS USM