Assuming optimum conditions, 50% survivorship to age 5.5, equal sex ratios, and using the oldest 

 documented female weaning her last litter at age 24.5 years, a single female would have the potential 

 capability of adding only three and one-half females to the population during her lifetime. Given a 

 normal rate of mortality for all age classes, a protracted reproductive cycle of 3.5 years to 7 years, and the 

 increasing stresses of habitat encroachment by humans, actual reproductive expectancy is usually far less. 

 Obviously, providing sufficient protection for females is essential to recovery and long-term population 

 management. 



Natural Mortality 



The causes of natural mortality for grizzly bears are not well known. Bears do kill each other. It is 

 known that adult males kill juveniles and that adults also kill other adults. Parasites and disease do not 

 appear to be significant causes of natural mortality but they may very well hasten the demise of 

 weakened bears. Natural mortality during the denning period is not well documented. Several authors 

 believe some bears die during denning, especially following periods of food shortages. However, few 

 such deaths have been recorded. 



Monitoring efforts conducted by USFWS scientists in the CYE, between 1999 and 2001, suggest that eight 

 grizzly bears died of natural causes during this time period. Seven of these eight mortalities involved 

 cubs. The increase in natural mortality beginning in 1999 may be linked to poor food production during 

 1998-2000. Huckleberry production during these years was about half the 11-year average. 

 Huckleberries are the major source of late summer food for bears in the CYE that enable them to 

 accumulate sufficient fat to survive the denning period and enable females to produce and nurture cubs. 

 Poor nutrition often results in failure to reproduce the following year. Poor food production may also 

 cause females to travel further for food, which may expose cubs to greater risk of mortality from 

 predators or accidental deaths. 



In the Swan Mountains during the period 1987-1996, nine grizzly bears died of natural causes. Two 

 causes included an adult female believed to be killed and fed upon by an adult male, and a female 

 accompanied by 2 cubs killed in an avalanche. 



Human-Caused Mortality 



Upon emergence from the den, bears move considerable distances from high, snow-covered elevations to 

 lower elevations to reach palatable, emerging vegetation on avalanche chutes, or to feed on winter-killed 

 or weakened ungulates on foothill winter ranges. Thiis type of movement often occurs on the Rocky 

 Mountain front region of Montana. Such movement of bears to lower elevations often takes them near 

 areas of human habitation, and may increase the incidence of human/bear conflicts. Similar mo\'ement 

 patterns often occur in the fall due to ripening of fruit and berries at lower elevations. This type of 

 movement occurs on the west front of the Mission Mountains in Montana. 



There are a variety of human-caused mortalities. Numbers of mortalities and their causes for the NCDE 

 and CYE are presented in Figures 6-9. These can be mistaken identit}' during legal black bear hunting 

 season, self defense, management removal of food habituated problem bears, collision with vehicles 

 and/or trains, or killing for malicious purposes. 



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