Most wildlife photo amateurs are very found of long focal length tele-lenses. Quite often, the ideal is to be able to go up to 400mm. However, ideally, we should have a zoom to adapt up from a shorter focal length. These last years, the technology evolved so significantly that there is no doubt the 100-400mm span appears as quite natural with an aperture never tighter than f/5.6 (Canon has it and Nikon has a 80-400mm zoom too). Sigma joins the competition with the 80-400mm f/4.5-5.6 EX DG OS.
The Digital Picture has a review of this Sigma lens that should be of interest to many wildlife photographers.