Bighorn Sheep in the Canadian Rockies: A History 1800-1970

Population fluctuations of bighorn sheep (Ovis canadensis canadensis Shaw) on the eastern slope of the Canadian Rockies and on the western slope in Kootenay National Park are discussed for the period 1800 to 1967. During pristine times bighorns underwent sporadic fluctuations caused by severe winters, disease, and changes in the condition of their ranges influenced by weather, fire and interspecific competition. Between 1860 and 1910, thousands of railway builders, miners, traders, settlers and resident Indians depleted numbers, by heavy indiscriminate hunting with firearms, from an original 10,000-plus to 2,600. Between 1910 and 1915, an extensive preservation program closed to hunting 7,500 square miles established as dominion reserves (now national parks) and reduced hunting to a low level on 6,500 square miles of sheep range in Alberta. This, together with improved range conditions resulting from fires and low sheep and elk numbers, tripled populations over the next 20 years to an estimated 8,500 by 1936. Between 1937 and 1949, a series of die-offs reduced populations to 2,500 by 1950. These die-offs were attributed to a pneumonia-lungworm disease, deteriorated ranges, heavy elk and livestock competition, decrease in grassland ranges caused by forest succession, and three severe winters between 1946 and 1949. By the summer of 1960, populations gradually increased to 10,100. Low numbers of sheep and elk during the early 1950's, mild winters, and a continued low level of hunting contributed to the increase. During fall and winter 1966-67, populations declined by 75% in Kootenay National Park because of deterioration of winter range, a pneumonia-lungworm disease and possibly, the after effects of the severe winter of 1964-65. However, populations on the eastern slope of the Rockies continued to increase in 1967, despite high loads of internal parasites and deterioration of winter range. On provincial lands, increased harvesting of bighorns and elk may avert a die-off. Future population levels will probably be determined by pneumonialungworm disease, harvests, and by range carryingcapacities, which will be affected by forest successional trends, climate, interspecific competition, and manmade modifications to the habitat.