Moose make up nine-tenths of an Isle Royale wolf's diet (the remainder being snowshoe hare and beaver). Moose in their prime years commonly outrun wolves in a hunt, especially on soft snow: moose can cross snow two feet deep at . Even if wolves can catch up to a moose, they cannot always bring it down; researchers often find wolves with hunting bruises and scars. To improve their chances, wolves pick out moose which are calves, old, diseased, or injured. The typical moose killed is about 12 years old and suffers from arthritis, osteoporosis, and/or periodontitis. Eighty to ninety percent of moose are brought down by wolves rather than directly by disease, and each wolf kills an average of between 0.44 and 1.69 moose per month.