CHAPTER 6 



ADULT MORTALITY 



Mortality Estimates 



Several methods were used to estimate mortality during 

 1976-1986: loss of marked deer, change-in-ratio, harvest 

 surveys, and differences between seasonal population 

 estimates. Prior to 1976, differences between population 

 estimates and harvest surveys were generally the only methods 

 available, though change-in-ratio techniques could also be 

 used during some years in the early 1960s. 



Each approach had some deficiencies. For example, only 

 small samples of marked deer were available during 1976-1979 

 and one death could make a 10-20% difference in estimated 

 mortality rate. Estimates based on those data were considered 

 only a general indication of high, moderate, or low mortality. 

 Regular capture and marking and increased samples each year 

 from 1979 through 1983 made mortality estimates based upon 

 marked deer more credible. After 1983, field work was less 

 intensive, few new deer were marked, and existing marked deer 

 came to represent an older age structure more susceptible to 

 mortality than the actual population. Those data tended to 

 overestimate mortality rates. 



Mortality estimates based on change-in-ratio are 

 dependent upon accurate field classifications (Conner et al. 

 1986). Although early winter classifications based on 

 observation of 60-80% of deer on the area were considered 

 accurate, summer-autumn classifications may have under- 

 represented females with fawns. Male: female ratios were 

 always higher in July than September-October. Females became 

 progressively more observable through summer and autumn, but 

 they may not have been equally observable as males during some 

 early preseason surveys. Also during some years, relatively 

 small samples of hunter-killed deer were available to 

 determine proportions of males and females harvested. 



Despite these considerations, the 3 estimates calculated 

 each year during 1976-1986 (Table 6.1) collectively provided 

 a reasonable range. Within that range, the final estimates 

 for all seasons and years (Tables 6.2 and 6.3) were those 

 which best fit observed populations trends. 



Female Mortality Patterns 



Annual mortality of adult females ranged from 2.2 to 

 43.0% and averaged 17.2% (Table 6.2). An average of 11.0% (0- 

 29.8%) of adult females alive on 1 June died during summer 



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