"Not all who wander are lost": Movements and ranges of grizzlies in the Greater Yellowstone & The story of Grizzly 480

Photo: Grizzly 480 pictured in the Lamar Valley during 2019. Picture courtesy of Jort Vanderveen.

Grizzly 480 was born sometime around 1996, somewhere in the confines of Yellowstone National Park. The Interagency Grizzly Bear Study Team (IGBST) first captured grizzly 480 at Cascade Creek, YNP, on October 8, 2004. His capture was part of the annual research and monitoring initiative set forth by the IGBST. During this initial capture, he was first marked and radio-collared. Two-days post initial capture grizzly 480 found himself back into the same trap; he was released on-site and not handled. Just short of one-year, on September 25, 2005, grizzly 480 was captured at Antelope Creek, YNP. The following year during 2006, grizzly 480 ‘shucked’ his collar (dropped). 

Photo: Grizzly 480 observed in the Lamar Valley during 2019. Picture courtesy of Jort Vanderveen.

Photo: Grizzly 480 observed in the Lamar Valley during 2019. Picture courtesy of Jort Vanderveen.

There was a hiatus in monitoring for grizzly 480; nearly 13-years elapsed until grizzly 480 made contact with IGBST researchers. On September 20, 2018, grizzly 480 was captured at Antelope Creek, YNP. During his handling, they collared him for research monitoring. Two weeks later, researchers captured grizzly 480 at Cascade Creek, YNP. Between his first and second captures in 2018, he cast his collar. At the time of the second subsequent capture, he was released and not handled (Haroldson et al. 2005, 2006, 2007, 2018)​

Figure: Map depicting capture locations of grizzly 480 (blue) and visual observations by visitors, observers (yellow) from 2004-2018.

Grizzly 480 displays traditional movements for a male grizzly bear in the Greater Yellowstone Ecosystem (GYE). Unlike females and females with cubs, males have much larger home ranges. Also, males do not display a high level of fidelity to their home ranges as females exhibit. Home range size is a function of resource availability; as sizes of home ranges decrease, habitat quality increases (Steiniger et al. 2010). A home range is defined as the “area traversed by the individual in its normal activities of food gathering, mating, and caring for young” (Burt, 1943). Home ranges are incredibly variable based on sex, age, and demographic groups. Several factors should be considered 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, they will roam widely in search of berries and food sources during late summer and autumn (dispersal, and motivated by food)
3.   They are not territorial (their home ranges do overlap!)
4.   Adult and subadult 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 (one of the slowest reproductive rates amongst all terrestrial mammals)

As mentioned, population density can greatly influence grizzly movements. In areas of high density or similar necessity for nutritional resources, ranges exhibited by female grizzlies are much smaller as opposed to those home ranges documented in low-density areas. This change is likely due to competition for space, and areas of frequent foraging; also the avoidance of dominant male grizzlies (Blanchard & Knight 1991, Dahle & Swenson 2003, Schwartz et al. 2003, Dahle et al. 2006, Edwards et al. 2013, Bjornlie et al. 2014). Patterns of movement are generally food driven; early spring, when bears first emerge from their dens, they will move to lower elevations in valley regions, where there is likely absence of snow, in efforts to find new green vegetation. Females with cubs-of-the-year (COY), however, will likely remain at higher, less preferred areas close to the den, due to the need for security of their cubs during a time of lacking mobility. As spring progresses, movements increase, and this stays true until the fall for most bears.

In the case of grizzly 480, an adult male grizzly bear, their movements generally peak during May & June. Daily activity and movement levels for both male and female grizzly bears typically peak during dawn or dusk, which we refer to as a “crepuscular activity pattern.” 

Despite significant changes in distribution, and the availability of specific food resources and habitat, lifetime home ranges did not change for male or female grizzly bears and remained consistent between 1975-1993 in comparison to 1994-2012.​

 Works Cited
 

1. Bjornlie, D. D., van Manen, F. T., Ebinger, M. R., Haroldson, M. A., Thompson, D. J. (2014). Whitebark pine, population density, and home-range size of grizzly bears in the Greater Yellowstone Ecosystem. PLOS ONE 9:e88160.
2. Blanchard, B. M., Knight, R. R. (1991). Movements of Yellowstone grizzly bears. Biological Conservation 58:41-67.
3. Burt, W. H. (1943). Territoriality and home range concepts as applied to mammals. Journal of Mammalogy 24:346-352.
4. Dahle, B., Stoen, O. G., Swenson, J. E. (2006. Factors influencing home-range size in subadult brown bears. Journal of Mammalogy 87:859-865.
5. Dahle, B., Swenson, J. E. (2003). Home ranges in adult Scandinavian brown bears (Ursus arctos): Effect of mass, sex, reproductive category, population density, and habitat type. Journal of Zoology 260:329-335.
6. Edwards, M. A., Derocher, A. E., Nagy, J. A. (2013). Home range size variation in female arctic grizzly bears relative to reproductive status and resource availability. PLoS ONE 8:e68130.
7. Haroldson, M. A., Dickinson, C., and B. E. Karabensh. 2019. Bear Monitoring and Population Trend. Pages 4-12 in F. T. van Manen, M. A. Haroldson, and B. E. Karabensh, editors. Yellowstone grizzly bear investigations: annual report of the Interagency Study Team, 2018. U.S. Geological Survey, Bozeman, Montana.
8. Haroldson, M. A., Dickinson, C., and D.D. Bjornlie. 2005. Bear Monitoring and Population Trend. Pages 4-10 in C. C. Schwartz, M. A. Haroldson, and K. West, editors. Yellowstone grizzly bear investigations: annual report of the Interagency Study Team, 2004. U.S. Geological Survey, Bozeman, Montana.
9. Haroldson, M. A., Dickinson, C., and D.D. Bjornlie. 2006. Grizzly Bear Capturing, Collaring, and Monitoring. Pages 4-10 in C. C. Schwartz, M. A. Haroldson, and K. West, editors. Yellowstone grizzly bear investigations: annual report of the Interagency Study Team, 2005. U.S. Geological Survey, Bozeman, Montana.
10. Haroldson, M. A., Dickinson, C., and D.D. Bjornlie. 2007. Bear Monitoring and Population Trend. Pages 4-7 in C. C. Schwartz, M. A. Haroldson, and K. West, editors. Yellowstone grizzly bear investigations: annual report of the Interagency Study Team, 2006. U.S. Geological Survey, Bozeman, Montana.
11. McLellan, B. N. (1989). Dynamics of a grizzly bear population during a period of industrial resource extraction. I. Density and age–sex composition. Canadian Journal of Zoology, 67(8), 1856-1860.
12. Munro, R. H. M., Nielsen, S. E., Price, M. H., Stenhouse, G. B., & Boyce, M. S. (2006). Seasonal and diel patterns of grizzly bear diet and activity in west-central Alberta. Journal of mammalogy, 87(6), 1112-1121.
13. Ross, P. I. (2002). Update COSEWIC status report on the grizzly bear Ursus arctos in Canada. Committee on the Status of Endangered Wildlife in Canada, Ottawa, 1-91pp.
14. Schwartz, C. C., Miller, S. D., Haroldson, M. A. (2003). Grizzly bear. Pages 556-586 in G. A. Feldhamer, B. C. Thompson, and J. A. Chapman, editors. Wild mammals of North America: Biology, management, and conservation. Johns Hopkins University Press, Baltimore, Maryland.
15. Steiniger, S., Timmins, T. L., & Hunter, A. J. S. (2010). Implementation and comparison of home range estimators for grizzly bears in Alberta, Canada, based on GPS data. In Proceedings of GIScience.