Population quality and bighorn sheep (Ovis canadensis canadensis Shaw)
Creators: name: Shackleton, David Maxwell
Publisher: name: University of Calgary
Year: 1973
Subjects: subject: QL 737 U5 S452 1973
subject: Sheep

description: Bibliography: p. 210-228.
description: The morphology, development and social behaviour of two popula­tions of bighorn sheep (0v-Ll cana.den/2-Ll canadeMi.6}, one stable in numbers and the other expanding, were used to examine the concept of population quality. Demographic state of a population was equated with its measure of quality. The stable population of the Cascade Valley, Banff National Park, Alberta, was taken as the poor quality population, while the sheep from Radium Hot Springs, British Columbia, were undergoing expansion and were regarded as the high quality population. Data were collected on behaviour of lambs from birth to three months of age, growth and dimen­sions of skulls and horns from the two populations and from four additional populations, and on social behaviour of the sheep from the two areas. Cascade Valley lambs suckled for significantly shorter periods, suckled more frequently but spent less total time obtaining milk, were refused more often in their attempts by their ewes, spent more time graz­ing and less tim?? playing, than their counterparts from Radium Hot Springs, all of which suggested the Cascade Valley lambs received less milk from their ewes. Ratios of 33 lambs and 67 lambs to 100 adult ewes were recorded in the poor and high quality populations, respectively. The pattern of annual horn qrowth and adult skull dimensions could be related to the condition of a population. Annual horn increments were initially longer in expanding pooulations but later the sheep appeared to be growing annually less horn than sheep from stable populations. This was partly due to the measure of horn growth used and to members of expanding populations growing faster. The largest adult skulls were from expanding populations. The mean life expectancy of rams from poor quality populations was longer than in rams from expanding populations. Horn growth was also found to vary within populations and was correlated with age at death and growth rate. Differences in lamb behaviour, horn and skull development led to the conclusion that there were significant environmental differences affecting the bioenergetic relationships of the populations. It was hypothesised that the differences in altitudinal range, together with climatic conditions, were responsible. Sheep from Radium Hot Springs wintered at lower elevations and migrated seasonally over greater alti­tudinal distances than Cascade Valley sheep and could, therefore, feed for a longer period on high quality growing vegetation. This occurred during the critical period of gestation and the annual growth cycle. The consequences of these differences were discussed. Social behaviour and organisation of the two study populations were similar in general, and based upon the same social order determined by horn size and sex. However, differences occurred in the degree to which the members of the two populations adhered to the rules of social conduct. Sheep from the expanding populations were socially more active. The age at social maturation was advanced among males from the expanding population and was attributed to differences in growth rates and in the density and composition of the populations. Herding of females by males, recorded only once before in mountain sheep, was observed at Radium Hot Springs. The variation found in behaviour between the populations was hypothesised to be the result of differences in the numbers and composition of the two study populations.