Winter has traditionally been the limiting factor for many wildlife populations in B.C., and represents a season with the potential to devastate animal populations one year and exert minimal influence the next. Winter may put a strain on mule deer populations in various ways. Snowfall acts as a barrier to forage availability, with a decreased food supply having particularly negative effects when compounded with other sources of stress. Herd productivity may be influenced and even if natality is reasonably high following a severe winter, malnourished and weakened animals will produce similarly unhealthy offspring with minimal chance for survival. Water may be in short supply in winter, and deer may be driven to eat snow to prevent dehydration, expending energy melting the snow with body heat. Mule deer tend to congregate on discrete winter range during times of particularly poor weather; bad conditions cause them to seek the shelter of forested areas and sunlit slopes and as harsh weather continues, large groups of animals become concentrated in limited areas and become dependent on a finite food supply. The possibility of predicting the influence of winter severity on mule deer populations by examining various climatic variables forms the basis for development of a winter severity index. This paper deals with the development of an index based on both standard climatic data and monthly values that reflects the severity of a given winter on mule deer. It focuses on the consequent management implications of applying the index to the various provincial deer management areas (DMA's) (it combines habitat capability information with parameters of the winter severity index in order to determine appropriate harvest regimes for each DMA). Limitations of the index and possible improvements are discussed followed by a brief reflection on the true value of the winter severity index.
Quayle, J., Ian Hatter. 1990. The Development and Applications of a Winter Severity Index for Mule Deer in British Columbia. Ministry of Environment