3. SUMMARY OF GRIZZLY BEAR BIOLOGY 



Physical Characteristics 



Grizzh' bears are generally larger than black bears and can be distinguished by longer, curved front 

 claws, humped shoukiers, and a face that appears concave (Figure 5). A wide range of coloration from 

 light brown to nearlv black is common. Guard hairs are often paled at the tips; hence the name "grizzly". 

 Spring shedding, new growth, nutrition, and climate all affect coloration. 



In the lower 48 states, the average weight of grizzlies ranges from 400-600 pounds for males to 250-350 

 pounds for females. Males may occasionally reach 800 to 1,000 pounds. Differences in body mass 

 between males and females are influenced by factors such as age at sexual maturity, samples from within 

 the population, season of sampling, reproductive status, and differential mortality. 



Body mass is dynamic in grizzly bears and varies seasonally. During late summer and fall, grizzlies gain 

 weight rapidly, primarily as fat when they feed intensively prior to denning. Because bears rely solely on 

 their stored energy reserves during hibernation, this pre-denning weight gain is essential for 

 reproduction and survival. Peak body mass generally occurs in fall just prior to hibernation. Bears 

 metabolize fat and muscle during the denning period. 



Grizzly bears are relatively long-lived, and individuals are known to have lived 40 years in the wild; a 

 captive bear lived 47 years. In general, the oldest age classes are listed at 28 years for males and 23 years 

 for females, although individuals can live longer. For example, in 2005, Kasworm and colleagues 

 documented a female grizzly bear in the Cabinet Mountains that lived to be 37 years old. 



Social Organization and Behavior 



Adult bears are individualist in behavior and normally solitary wanderers. Except when caring for 

 young or breeding, grizzly bears have solitary patterns of behavior. Individuals probably react from 

 learned experiences. Consequently, two individual bears may respond in opposite ways to the same 

 situation. Strict territoriality is unknown, with intraspecific defense limited to specific food 

 concentrations, defense of young, and surprise encounters. 



Each bear appears to have a minimum distance within which another bear or person cannot enter; any 

 intrusion of this distance may evoke a threat or an attack. Surprise is an important factor in many 

 confrontations involving bears and humans. A female with young exhibits an almost reflexive response 

 to any surprise intrusion or perceived threat to her "individual distance" or that of her cubs. Defense of a 

 food supply is another cause of confrontation between humans and bears. Bears generally defend a kill or 

 carrion out of perceived need. 



Grizzly bears of all ages will congregate readily at plentiful food sources and form a social hierarchy 

 unique to that grouping of bears. Mating season is the only time that adult males and females tolerate 

 one another, and then it is only during the estrous period. Other social affiliations are generally restricted 

 to family groups of mother and offspring, siblings that may stay together for several years after being 

 weaned, and an occasional alliance of sub-adults or several females and their offspring. 



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