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An ecological study of California bighorn sheep Ovis canadensis californiana (Douglas) in southern British Columbia Blood, Donald Arthur

Abstract

There have been alarming declines in the number of California bighorn sheep in the Similkameen region of British Columbia since the latter part of the nineteenth century. Present conflict for food supply with domestic stock makes further herd reduction imminent. This study was initiated to gather sound ecological data on which to base management and conservation practises for the California bighorn sheep in British Columbia and to determine population status of the Ashnola herd. The Ashnola herd was studied in the field from May 1960 through June 1961. The study area is described on the basis of broad soil and vegetation patterns. Line point transects were employed to determine botanical composition of important winter ranges. The sheep population is analysed from age and sex ratios and age structure data. Age structure was determined by collecting remains, in the field, of sheep which died of natural causes. Natality and mortality rates from the above sources indicate that the herd is relatively stable. Census data substantiates this observation. Factors limiting population increase are evaluated with emphasis on competition for food. Predation, accidents and hunting are not considered to be presently limiting herd increase. Incidence of parasitism in the herd was investigated by post mortem examination and fecal analysis. No deaths directly attributable to parasitism were noted during the study. Grazing by cattle appears to be the primary land use presently threatening the welfare of the herd. Bighorn sheep-cattle competition involves spring and fall utilization by cattle of sheep winter ranges. Direct and indirect observation of animal distribution, food habit analysis and exclosure plot technique have been employed to evaluate the competitive interaction. Although competition was slight in 1960, food shortage resulting from cattle grazing and occasional severe snow conditions is suggested as the factor limiting herd increase. Aspects of herd biology and behavior such as rutting, lambing, migration and social organization are also described. Management considerations and recommendations are briefly discussed.

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