(0 



r 

 o 



50- 

 45- 

 40- 

 35- 

 30- 

 25- 

 20- 

 15- 

 10- 

 5- 



o-^ 



• Total Mortality 



o Hunting Mortality 



o-- Natural Mortality 



40 47 



3 4 5 6 7 8 9 10-11 12 + 

 Female Age at Start of Year 



53 55 55 43 27 22 20 27 15 

 Sample Size 



Figure 6 . 1 



Age-specific mortality rates for female mule deer 

 in the Missouri River Breaks, Montana, 1976-1986. 



Except in the very best years, lactating and rearing 

 fawns to 6 months of age probably draws on body reserves in 

 addition to nutrition provided by current forage. Forage 

 quality is often insufficient to fully replace body reserves 

 following weaning, and on average, body reserves have reached 

 a critical level following weaning in the fifth reproductive 

 year. The more fawns a female has recruited during her first 

 5 reproductive years (cumulative reproductive stress), the 

 poorer her condition at age 6 and the greater her 

 vulnerability to death. Many females that do not die at 6 

 years either do not have fawns the next year or lose them 

 shortly after parturition. This gives them the opportunity to 

 recover body reserves, such that survival and fawn recruitment 

 among 8+ year olds improves over that at 6 years. 



Reproductive histories were available for 7 of 9 females 

 that died between age 6 and 7 from non-hunting causes. All 

 had recruited fawns to weaning age at above average rates 

 during the years leading up to their death. Four of the 7 had 

 weaned fawns during the year of their death and for at least 

 2 years prior to that. The reproductive status for 2 was 

 unknown during the year of their death, but they had both 

 weaned fawns for at least the 2 years prior to their death. 



163 



