A Weather Severity Index on a Mule Deer Winter Range

Donavin A. Leckenby, Arthur W. Adams
1986 Journal of range management  
Temperature, wind, and snow conditions predictably affect the nutrition, behavior, distribution, productivity, and mortality of free-ranging cattle and big game in winter. Indexing of data obtained with commonly available weather instruments to reflect episodes of positive and negative energy balances of free-ranging ruminants could aid scheduling of feeding programs and planning of cover-forage manipulations. Such a weather severity index was developed and tested over 11 winters. Plausible
more » ... ters. Plausible levels of stress and episodes of reiative severity were depicted during winters when mule deer exhibited low, moderate, and high mortality. The index curves mirrored over-winter deciines of fat reserves probably sustained by mule deer. Lesser weather severity was predicted and measured in a western juniper woodland than in an adjacent rabbitbrush steppe community in southcentrnl Oregon. Review of literature on ruminant physiology, microclimate, habitat structure, and diet quality suggested that productivity and survival of free-ranging ruminants could be predicted from interrelationships among those factors. Therefore, animal performance would likely be improved by managers who provided domestic and wild ruminants with shelter, to moderate effects of weather, or with a readily digestible diet, to satisfy nutrient requirements (Brody 1956 , Short et al. 1969 , Silver et al. 1971 , Verme and Ozoga 1981 , Robbins 1983 ). Specific physiological responses, feeding efficiencies, behavioral reactions, and distribution patterns of deer and cattle appear related to levels of temperature, wind, radiation, and snow (Wallmo and Gill 1971, Holter et al. 1975, Subcommittee on Environmental Stress 1981 , Finch et al. 1982 . Nutrient balance, feed intake, heat production, and growth rate monitored under controlled conditions indicate domestic and wild ruminants utilize similar physiological strategies to endure adverse weather and yet remain productive (Moen 1968a, Nordan et al. 1970 , Robinette et al. 1973 . Structural elements of vegetation predictably influence microclimates to which free-ranging livestock and wildlife may be exposed. Geiger (1966) described how grasslands, shrublands, and forests created microclimates for animals. Reifsnyder and Lull (1965) developed models that predict temperature, radiation, and snow depth from independent variables such as tree height and crown closure. Gifford (1973) documented how radiation and wind speed changed when structures of pinyon-juniper (pinus spp. and Juniperus spp.) stands were altered by chainings. Indices of severity have been used to relate weather conditions to responses of free-ranging deer. Verme (1968, 1977) found distribtuions, growth, survival, and mortality were correlated with an index derived from the chilling rate of air and the depth and hardness of snow. Roper and Lipscomb (1973) and Picton (1979) associated winter severity and climate indices with losses of deer. Converting temperature, wind, and snow data to weather severity indices may help develop management strategies to enhance feeding efficiencies and animal performance. We describe indices derived from temperature hours, wind speeds, and snow cover and depths measured on a range grazed by cattle in spring and fall and by mule deer (Odocoileus hemionus hemionus) in winter. The
doi:10.2307/3899059 fatcat:arjjflq7trfnvboxfo6vrofhya