was also made of ponderosa pine needles. Despite this, 

 mortality, especially of adults, was relatively light during 

 those winters and fawn mortality was less than during some 

 milder winters. 



Overall, it appeared that rabbitbrush was the preferred 

 winter forage and that use of big sagebrush and Rocky Mountain 

 juniper increased only as a result of declining availability. 

 Similar conclusions were made by Dusek (1975) for mule deer 

 north of our study area. These conclusions may be consistent 

 with Nudds (1980) hypothesis that deer are forage generalists 

 when winter conditions are severe. 



Spring 



Use of forbs increased throughout spring and reached an 

 annual peak during May. Shrub use usually declined by late 

 March when "green-up" of new growth was initiated, though in 

 some years "green-up" did not begin until early April. Use of 

 grasses increased when new growth was initiated and reached an 

 annual peak of around 20% of the diet in April, declining 

 thereafter as forbs became more abundant. The major grass 

 species used during spring was Sandberg bluegrass . Important 

 forbs used during spring were bastard toad flax (Comandra 

 umbel latum) , wild onion (Allium textile) , oyster plant 

 (Tragopogon dubius) , wild parsley (Musineon divaricatum) , 

 lomatium (Lomatium foeniculaceum) , and American vetch (Vicia 

 americana ) . 



Discussion 



Green, succulent forage was preferred whenever it 

 occurred. When sufficient late summer and/or autumn rainfall 

 and relatively warm autumn temperatures resulted in 

 maintenance of succulence of forbs or promoted regrowth of 

 forbs and grasses, use of normal autumn browse species was 

 delayed. These autumn browse species, especially rubber 

 rabbitbrush, were then available for longer periods into 

 winter. Heavy dependence by mule deer on Rocky Mountain 

 juniper and big sagebrush was delayed further into winter. An 

 autumn green-up prolonged the period of good to adequate 

 nutrition not only through autumn, but into winter. 

 Conversely, drought led to earlier maturation and desiccation 

 of all herbage and in turn to heavy utilization of preferred 

 browse, decreasing its availability during winter. Generally, 

 a shorter winter season occurred on our study area than in 

 most mountainous areas of the Rocky Mountains. Regrowth often 

 began by late March although it was sometimes delayed until 

 mid-April . 



During occasional winters of deep, continuous snow cover, 

 much of the area was not inhabitable by deer. Many deer using 



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