Observational home ranges: GB 815

Photo credits: Jim Peaco (left) & Neal Herbert (right) (NPS, 2017)

​GB 815 was first captured by the Interagency Grizzly Bear Study Team June 10, 2015 and fitted with a VHF radio-collar for research purposes. At the time of her capture, no cubs were present. The following year, 2016, she was observed with an initial litter of three cubs-of-the-year (COY); by the end of 2016 she only had one remaining cub.
 
During 2017, GB 815 was observed in six different months (April, May, June, July, August, September) for a total of 36 observations. She was occupied with one-remaining yearling cub from her initial litter of three during 2016. Her range encompassed approximately 123 km^2 during 2016. This nearly doubled during 2017, where her range was approximately 225 km^2.
 
Home range size has often been thought to be a function of resource availability; as sizes of home ranges decrease, habitat quality increases (Steiniger et al. 2010).
 
Several factors must be taken into consideration with the construction of home ranges for grizzly bears (Munro et al. 2006, Ross 2002, McLellan 1989).

1. Grizzlies are omnivorous and eat primarily vegetation.
2. Often times, they will roam widely in search of berries and food sources during late summer and autumn
3. They are not territorial.
4. Males will have home ranges known to be several times larger than that of females.
5. Home range is directly impacted by population density
6. Bears may move hundreds of kilometers during dispersal.
7. Grizzlies are known to avoid some environments such as high elevations with rocks, snow, mainly because of limited food, however, that does not exclude them crossing such an environment.
8. Grizzlies are slow to mature and reproduce.

 
Ultimately, it is possible that some females never meet or attain a maximum home range size within the Yellowstone grizzly population, given the unpredictability of food resources (Mattson et al. 1991). This was also demonstrated during a 13-year study performed by Blanchard et al. 1991, where several females were monitored 6-years or more and had not attained a maximum or reflective maximum home range.
 
The movements of females with COY for example, can be explained by several factors. Movements of females with COY during spring may be due to the lack of mobility of the young, when they are also most vulnerable to predation (Blanchard et al. 1991). Females with COY typically have increased security for their young during spring by selecting habitats, and least preferred vegetation at higher elevations, while other bears in cohorts are found at lower, more productive elevations (Blanchard et al. 1991). Females with cubs may be displaced due to sub ordinance of the female to other bears in a very similar proximity, or even the ignorance of vulnerability of her cubs to predation, stemming from lack of experience (Blanchard et al. 1991).