Declines of Bighorn Sheep, Ovis canadensis, on Deteriorating Winter Range in Jasper National Park, Alberta, 1981-2010

Abstract

Bighorn Sheep (Ovis canadensis) wintering in the lower Athabasca River valley of Jasper National Park, Alberta, were monitored from 1981 to 2010 by recording maximum band sizes per annum on two traditional but separate sheep ranges. In study area #1, the ram band declined significantly from a 20-year mean of 18 in the period 1981-2001 to a 5-year mean of 11 in the period 2001-2006, with a slight recovery in 2006-2010. Ewes in area #1 dwindled from a mean of 20 in the period 1981-1995 to zero in the period 1995-2010. In area #2, the ewe band dropped significantly from a mean of 40 in the period 1981-2001 to 24 in the period 2001-2010. The declines in area #1 coincided with an invasion of Russian Thistle (Salsola kali). Range conditions in area #2 deteriorated following four years with lower than average annual precipitation. The mean lamb:ewe ratio in area #2, pooled for 29 years, was 22:100 (n = 646). The sheep were protected from hunting, but were subject to a full range of indigenous carnivores. However, predation did not appear to be the primary cause of the declines, nor was competition for forage with American Elk (Cervus elaphus).