Survival of fawns was not greater than average during 

 summer 1982, but little mortality occurred after microtine 

 populations began to increase during late summer. Fawn 

 survival was high during summer 1983 but declined 

 substantially after microtine and jackrabbit populations 

 "crashed" in late autumn. 



Drought conditions prevailed from late summer 1983 

 through late summer 1985. Both fawn survival and alternate 

 prey populations were low during that period. 



Survival increased substantially for the 1986 and 1987 

 fawn cohorts, coinciding with improved forage conditions 

 initiated by heavy rains and an autumn "green-up" of 

 vegetation during 1985. This was followed by an irruption and 

 subsequently high microtine population from summer 1986 

 through autumn 1987. 



Fawn Mortality in Relation to Winter Severity 



Mortality of fawns during winter varied greatly among 

 years (Table 5.5). Multiple regressions did not indicate a 

 linear relationship between winter severity one year and 

 survival of the subsequent fawn cohort. Winter severity and 

 fawn mortality during the same winter were positively related 

 (r = 0.44, P < 0.05, N = 27), but the relationship had many 

 exceptions . When 5 years that deviated most were omitted from 

 the regression, the relationship between winter severity and 

 fawn mortality strengthened (r = 0.655, P < 0.01, n = 22). 



Although winter fawn mortality might generally increase 

 with winter severity (Fig. 5.14), prediction of fawn mortality 

 based on winter severity alone could result in erroneous 

 conclusions. Fawn mortality during the 2 most severe winters 

 on record, 1977-78 and 1978-79, was about half that of 5 other 

 winters, including 1975-76 and 1983-84, which were about 20% 

 below the mean for winter severity. Winter severity was only 

 slightly above the mean during 1984-85, but fawn mortality was 

 the highest recorded. For most years when winter severity was 

 near or below the mean (11.2), fawn mortality appeared to vary 

 randomly between 4 and 30%. The winter severity index varied 

 from below average (9.2) to very high (26.1) during winters 

 when catastrophic mortality occurred. 



Prior forage conditions helped explain some anomalies in 

 the in the relationship between fawn mortality during winter 

 and winter severity. Fawn mortality was high during winter 

 1964-65 despite only slightly more than average numbers of 

 deer. However, forage quantity and quality were below average 

 (Fig. 3.9) during summer 1964 and, although forage conditions 

 were above average during summer 1963, they also were below 



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