Effect of Snow Depth on Predation and Scavenging by Gray Wolves

Snow can affect wolf predation rates, diet composition, and scavenging, which are important components in understanding and managing wolf-prey systems. Thus, I located elk (Cervus elaphus) killed by gray wolves (Canis lupus, hereafter referred to as wolves) in Banff National Park, Alberta for 5 winters, and I followed one pack of wolves intensively throughout 1 winter to determine the effects of snow depth on wolf predation. Kill rate increased (P < 0.001) from 1 ungulate/5.4 days with no snow to 1 ungulate/1.1 days in snow 60 cm deep. Similar (P > 0.5) numbers of calves (n = 24) and adults (n = 28) were killed in shallow snow; predominantly calves (9 of 11) were killed at intermediate snow depths that hindered calves but not adults; and only adults (n = 9) were killed in deep snow that hindered both age classes of elk. Scavenging of ungulate carcasses occurred at shallower (P < 0.01) snow depths than did kills. At shallow snow depths, wolves likely encountered carcasses more frequently because they had a lower kill rate and moved farther between kills. My data indicate snow depth could add substantial, density-independent variation to wolf-prey interactions and affect which classes of prey are killed.