Winter severity during 1971-72 was similar to 1968-69; 

 however, the number of deer in the population entering winter 

 was above average. Catastrophic mortality of fawns and 

 substantial mortality of adults occurred. Forage conditions 

 were below average during each of the 3 previous summers (Fig. 

 3.9) and fawn production and survival had been high during the 

 late 1960s suggesting both general body condition and fat 

 reserves of deer were probably low at the onset of winter. 



The winter severity index was the highest on record 

 during 1977-78 and 1978-79, yet fawn mortality was moderate 

 (Fig. 5.14). Although forage conditions were below average 

 during early summer 1977, a late summer "green-up" enabled 

 deer to feed on high-quality forage for about 3 months prior 

 to the onset of winter. Deer numbers were low and deer were 

 in good condition entering winter. Forage conditions were 

 excellent during summer 1978, deer numbers were low, and deer 

 continued to build body condition and fat reserves and were in 

 good condition at the onset of winter 1978-79. Although 

 moderate fawn mortality occurred during winters 1977-78 and 

 1978-79, it was much less than was expected considering 

 mortality that occurred during winters of equal or lesser 

 severity (Fig. 5.14). 



Snow depth, which seldom exceeds 30 cm here, was greater 

 than 75 cm more than 2 months during 1977-78 and exceeded 60 

 cm for more than 2 months during 1978-79. Persistent winds 

 caused much drifting of snow and many shallow drainages were 

 filled. Thus, snow depth precluded use by deer of most of the 

 southern portion of the area. Even in areas where deer 

 occurred, much of their normal food was inaccessible. 

 Significant use of ponderosa pine needles by deer was detected 

 only during those winters. Deer could only have survived by 

 utilizing well-developed fat reserves. 



Winter 1983-84 was slightly below average in severity and 

 winter 1984-85 was only slightly above average in severity, 

 but fawn mortality was catastrophic during both winters; many 

 adult females also died during 1983-84. Numbers of deer were 

 above average at winter's onset during each of the 2 years. 

 Also, forage conditions were below average for 3 of 4 summers 

 preceding winter 1983-84, and for 4 of the 5 summers prior to 

 winter 1984-85. Fawn production and survival was high 

 starting in 1978, and continued relatively high through early 

 1983, which probably required mobilization of body reserves 

 during 1982 and 1983. Because of dry conditions during late 

 summer and autumn 1983, deer probably entered winter in poor 

 condition, with very low fat reserves. 



The effect of winter severity on deer mortality appeared 

 to be influenced by prior forage conditions. Numbers of deer 



148 



