and/or a "green-up" of grasses occurred. Snowberry ranked 

 second in both use and occurrence among species used during 

 autumn. Its use was especially heavy during good fruit- 

 bearing years when the berries were probably a source of high 

 energy. Rose, while not usually a major food item, was used 

 consistently and was also most heavily used when rose hips, 

 possibly high in energy (Welch and Andrus 1977), were 

 abundant. Use of fragrant sumac was usually negligible after 

 leaf drop in September. Autumn use of Rocky Mountain juniper 

 and big sagebrush was relatively minor, but was more important 

 when sweetclover or green grasses were not available. 



Winter 



More than 80% of the diet during winter consisted of 

 shrubs during most years. Use of forbs was generally low 

 except during periods of deep snow, when desiccated forbs, 

 protruding above the snow, were eaten, and during warm, 

 snow-free periods, when some forbs "greened up" on 

 south-facing slopes. Grasses were generally used only during 

 late March as new growth started. 



Forage use during winter usually depended upon 2 major 

 factors: snow depth and forage use during autumn. Big 

 sagebrush and Rocky Mountain juniper were major forage species 

 during winter in either case. Rabbitbrush was preferred and 

 heavily used whenever it was available, but deep snow reduced 

 both availability and use. Essentially, all current annual 

 growth of rabbitbrush was utilized each year. When green 

 forage was available during autumn and use of rabbitbrush was 

 reduced, much of the use of rabbitbrush was delayed until 

 early winter, when it received heavy use. Use of rabbitbrush 

 then declined through winter as use reduced availability. 

 Rabbitbrush may be depleted earlier in winters with high deer 

 populations than during winters with low populations . 

 Approximately 28% of the diet was rabbitbrush during February 

 1977 (470 deer), 20% during February 1980 and 1981 (1020-1030 

 deer), and only a trace during February 1984 (1545 deer). 

 However, the latter periods also coincided with dry 

 conditions, leading to heavy autumn use of rabbitbrush. 



There was more than 30 cm of snow on the ground for 97 

 and 112 days and more than 45 cm of snow on the ground for 85 

 and 96 days during winters 1977-78 and 1978-79, respectively. 

 Winter 1981-82 was less severe than either 1977-78 or 1978-79, 

 nevertheless, snow depth was 23 cm or more for 58 days. 

 Rabbitbrush was essentially unavailable those winters and 

 received little use regardless of population level (Table 

 9.2). Fragrant sumac was also largely unavailable and was 

 used much less than in more open winters. Rocky mountain 

 juniper and big sagebrush were heavily used and very heavy use 



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