Reproductive Biology of White-Tailed Deer in Manitoba

Abstract

This study is based on 159 female white-tailed deer (Odocoileus virginianus) collected during the winters of 1961, 1962, and 1963 from, in order of decreasing habitat quality, the Turtle Mountain, Duck Mountain, and Whiteshell areas of Manitoba. Conception rates were high for adults and yearlings but relatively low for fawns. Ovulation rates and average numbers of fetuses per pregnant doe were high for adults from all areas but the ovulation rate was significantly higher for adults from Turtle Mountain. Both rates were high for yearlings from Turtle Mountain but relatively low for yearlings from the Whiteshell and Duck Mountain. Considering all age-groups, fertility was highest in Turtle Mountain, followed by Duck Mountain, and lowest in the Whiteshell. The rate of ova loss among adult does from Turtle Mountain was significantly higher than among adults from the other areas. This may be due, indirectly, to flushing. Kidney fat indices showed that deer from all areas lost condition at the same rate during winter. A general comparison of winter environment between the Whiteshell, which was closed to hunting, and the Upper Peninsula of Michigan indicates that lower temperatures in the Whiteshell cause deer there to suffer more from malnutrition during average winters than do deer in the Upper Peninsula and hence to have relatively higher numbers of stillbirths and postnatal losses of fawns. Lighter snowfall in the Whiteshell allows deer to cover more of their summer range in winter than do Upper Peninsula deer, thus helping to explain why over-utilization of browse in the Whiteshell is not the serious problem it is in the Upper Peninsula. Winter weather appears to be sufficient to prevent deer irruptions in the Whiteshell and to hold maximum density well below that reached in the Upper Peninsula. It is postulated that similar controls function in the rest of Manitoba. White-tailed deer in Manitoba have a high level of fertility but densities are relatively low compared with most good deer areas in the United States. Irruptions, characterized by severely decreased size and fertility; the formation of browse lines; prevention of forest regeneration; and eventual mass die-offs, do not occur in Manitoba, apparently because winter environmental conditions during average years result in over-winter losses and an unusually high percentage of stillbirths and postnatal losses of fawns. Consequently the average annual increment is relatively small. This study was undertaken in 1960 with the support of the Manitoba Wildlife Branch and was completed in fulfillment of research requirements for a M.Sc. degree from the University of Alberta. I wish to express sincere gratitude to Eugene F. Bossenmaier, Chief Biologist, Manitoba Wildlife Branch, for suggesting the study initially, for his continued advice and encouragement, and for his helpful criticisms of this manuscript. Sincere gratitude is also extended to Dr. W. A. Fuller and to Dr. J. C. Holmes, Department of Zoology, University of Alberta, for their guidance during the final year of the study and for their criticisms of the manuscript. Dr. W. G. E. Evans, Department of Entomology, University of Alberta, also gave helpful criticisms. Special thanks are extended to Conservation Officers of the Manitoba Department of Mines and Natural Resources who collected specimens for the study. Appreciation is expressed to Dr. G. I. Paul, Department of Statistics, University of Manitoba, for his advice on statistical analysis of the data. I also wish to thank L. J. Verme of the Michigan Department of Conservation for his comments on the manuscript.