Radioactive Bears and Wolves are highly modded variations of the vanilla bears and wolves.

There are 3 classes of these wolves and bears. They are: 
Tough (not used on our server)
Beast - Very difficult to kill. Yields 2 pelts each.
Juggernaut - Even more difficult to kill. Yields 4 pelts each.

Both animals exist ONLY on the island directly west of the arctic region. They do not spawn anyplace else on the map. Formerly they spawned at Camp Wolf and the Power Plant, but no longer.