type during all seasons. On the East Front, the day time cover types most important to grizzly bears were 

 closed timber, rock, prairie grassland, and aspen stands. 



Derming 



Western Montana grizzlies generally spend 5-6 months a year in dens. Most dens are excavated but 

 natural ones can also be used. Den digging can start as early as September or take place just prior to 

 entry in mid-November. Dens are usually dug on steep slopes where wind and topography cause an 

 accumulation of deep snow and where the snow is unlikely to melt during warm periods. Finding an 

 isolated area that will be well covered with a blanket of snow will minimize the escape of body-warmed 

 air and will provide a secure environment for a hibernation period that may last up to six-months. In 

 western Montana, dens typicallv occur at elevations between 5,900-6,600 feet and at slopes greater than 

 50% in open and open-timbered areas. Most den sites occur on western, northern, or eastern aspects. 



Generally, grizzlv bears den bv late October to mid-November and emerge in mid-March to Late April. 

 Females with young typically are the first to enter dens and the last to emerge in the spring, while males 

 usually are the last to enter and the first to emerge in the spring. In the Swan Mountains, males have 

 entered their dens as late as mid-December and females with cubs have been known to emerge as late as 

 mid-May. In the Yaak River, male grizzly bears typically enter dens during December with many 

 individuals remaining active until late December. 



Securitv at den sites appears to be an important management consideration, especially if human 

 disturbance occurs near the time of den entry. There has been some concern of the possible effects of 

 snowmobiles on denning bears. This is increased with increasingly powerful snow machines and the 

 practice of "high marking" which could occur in denning habitats. A study in northwestern Montana did 

 not observe any overt effects of snowmobiles within 1.5 miles of dens. The greatest potential impact on 

 bears was during spring when females with cubs were still confined to the vicinity of the den, and also 

 after bears had moved to gentler terrain more suitable to use by snow machines. Predictable denning 

 chronology and the behavioral plasticity bears exhibit toward den and den site characteristics suggest 

 potential human impacts to denning grizzly bears may be mitigated by careful consideration when 

 implementing strategies for human activity'. 



Home range 



In the CYE, adult male grizzly bear life ranges recorded by various USFWS researchers between 1983 and 

 2004 averaged 457 mi- while female life ranges during the same period averaged 204 mi-. Female 

 offspring generally establish home ranges around their maternal range. 



On the East Front, females with cubs were found to restrict movements compared to years when they did 

 not have cubs. The ability to confine activities during years with cubs may depend upon habitat 

 conditions and the distribution of food resources, and may impart survival advantages to these litters. 



In the Swan Mountains, core area of home ranges varied by sex and time of year. Core areas for males 

 were larger during the early season relative to the late season. The converse was found for females. The 

 larger core size for males during the early season may be due primarily to increased movements by 

 reproductively active males during the breeding season. The extent of early season movements for 

 females each year depended on whether they had young, and the age of the young. During the late 

 season male core areas were smaller; a result of more restricted and concentrated foraging behavior. 



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