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The Ways That Yellowstone's Grizzly Bears Are Unique

Here is a partial account of the many ways that Yellowstone’s grizzly bears are unique in the behaviors they exhibit and the foods they eat—not only in North America, but also globally.

A very brief description of the food and associated behavior is given, followed by some key references.
1) Geophagia (dirt eating): This behavior has not been documented for grizzlies or brown bears anywhere else in the world. The bears eat dirt excavated from highly specific sites in geothermal areas where the soil has elevated potassium and sulfur content. The geophagy occurs only during early spring, shortly after the bears emerge from their dens. They probably eat the dirt to replenish potassium lost during hibernation, before widespread green-up occurs (green foliage is normally a ready source of potassium). The sulfur may also be therapeutic in stimulating the digestive tract after 6 or so months of dormancy.

Mattson, D.J., G.I. Green & R.A. Swalley  (1999).  Geophagy by Yellowstone grizzly bears. Ursus 11: 109-116.


2) Consumption of pondweed roots (Potamogeton sp.): Grizzlies are not known to dig the roots of this plant anywhere else in North America. The only other location where brown bears might have dug pondweed roots is around Lake Baikal in Siberia. Almost all of the known excavations in Yellowstone are within the Yellowstone caldera on rhyolite substrate. Pondweed roots are dug during mid to late fall from the bottoms of vernal ponds that have drained and dried after being inundated during the spring and early summer.

Mattson, D.J., S.R. Podruzny, & M.A. Haroldson  (2005).  Consumption of pondweed rhizomes by Yellowstone grizzly bears. Ursus 16: 41-46.


3) Consumption of sweet cicely roots (Osmorhiza sp.): Bears elsewhere are known to graze sweet cicely foliage, but not dig its roots. Root digging typically occurs during fall at elevations >7000’ and possibly with increasing frequency during recent years.

Mattson, D.J.  (2000).  Causes and Consequences of Dietary Differences Among Yellowstone Grizzly Bears (Ursus arctos).

Ph.D. Dissertation, University of Idaho, Moscow, ID.  173 pp.


4) Consumption of yampa roots (Perideridia gairdneri): Grizzlies in Yellowstone are the only ones known to excavate this scrumptious root in moist meadows, typically at mid elevations. Grizzly bears in other regions to the south and west also probably dug this root food prior to being extirpated, but Yellowstone is the only place where the behavior continues. This root was also extensively dug by Native Americans.

Mattson, D.J.  (2000).  Causes and Consequences of Dietary Differences Among Yellowstone Grizzly Bears (Ursus arctos). Ph.D. Dissertation, University of Idaho, Moscow, ID.  173 pp.


5) Consumption of biscuitroots (Lomatium cous and L. triternatum): Grizzlies elsewhere may dig this root, but not anywhere as intensively as in Yellowstone. Lomatium cous in particular occurs from low elevations (c. 6800') up into the alpine, with flowering occurring progressively later with increasing elevation. Bear digging correspondingly tracks peak flower from low to high elevations, beginning in April and ending sometime in July or early August. Almost all the excavations occur on rocky ridges on west to southwest-facing slopes. This root was also extensively dug by Native Americans.

i. Mattson, D.J.  (2000).  Causes and Consequences of Dietary Differences Among Yellowstone Grizzly Bears (Ursus arctos).  Ph.D. Dissertation, University of Idaho, Moscow, ID.  173 pp.
ii. Mattson, D.J.  (1997).  Selection of microsites by grizzly bears to excavate biscuitroots.
Journal of Mammalogy 78: 228-238.


6) Consumption of pocket gophers (Thomomys talpoides) and their root caches: This feeding behavior has not been documented for grizzlies anywhere else in the world although, as with yampa digging, grizzlies farther to the south no doubt engaged in this behavior prior to being extirpated. Excavation of pocket gophers is concentrated in the spring during and shortly after snowmelt when saturated soils restrict gophers and their caches to shallow depths. However, excavations continue into mid to late summer and tend to be progressively deeper.

Mattson, D.J.  (2004).  Consumption of pocket gophers and their food caches by grizzly bears.  

Journal of Mammalogy 85: 731-742.


7) Excavation of vole (Microtus sp.) root caches: Voles in parts of Yellowstone are somewhat unique among voles in temperate regions of North America in making root caches that grizzly bears occasionally excavate during the fall. There are no records of grizzlies excavating vole root caches with the possible exception of some observations from Alaska.

Mattson, D.J.  (2004).  Consumption of voles and vole food caches by Yellowstone grizzly bears:

exploratory analyses.  Ursus 15: 218-226.


8) Excavation of earthworms: Grizzlies have been documented excavating and eating earthworms only in the Yellowstone region. There is no other record worldwide with the possible exception of the consumption of worms from underneath hay by brown bears in Russian Europe. Consumption of earthworms occurs in moist to wet meadows; all of the worms consumed are exotic species introduced from Eurasia. North America had an extremely depauperate earthworm fauna after the ice ages and non-native earthworms are slowly colonizing high elevation and high latitude regions throughout North America.

Mattson, D.J., M.G. French & S.P. French  (2002).  Consumption of earthworms by Yellowstone grizzly bears.  Ursus 13: 153-158.


9) Consumption of mushrooms, including false truffles (Rhizopogon sp.): Grizzlies in Yellowstone are unique in the extent to which they consume mushrooms, and the only bears from North America that have been documented to extensively consume false truffles. Most of the mushroom-eating is associated with lodgepole pine forests and most occurs during August through October.

i. Fortin, J. K., C.C. Schwartz, K.A. Gunther, J.E. Teisberg, M.A. Haroldson, M. A. Evans & C.T. Robbins  (2013). Dietary adjustability of grizzly bears and American black bears in Yellowstone National Park. The Journal of Wildlife Management 77: 270-281.
ii. Mattson, D.J., S.R. Podruzny & M.A. Haroldson  (2002). 
Consumption of fungal sporocarps by Yellowstone grizzly bears.  Ursus 13: 159-168.


10) Consumption of bison (Bos bison): Grizzlies in Yellowstone are the only bear population to still eat bison meat, and constitute a living museum of a behavior that was once widespread wherever grizzlies and bison coexisted. Almost all of the meat from bison is obtained by scavenging, and bison are disproportionately important in this regard because there is so much meat on them—enough to swamp most smaller scavengers, and with hides thick enough to also deter scavengers other than bears and wolves. Most bison meat is obtained during the spring from winter-killed animals, but there is a secondary peak in consumption during August-September associated with scavenging of bull bison that died during or shortly after the rut.

i. Mattson, D.J.  (1997).  Use of ungulates by Yellowstone grizzly bears Ursus arctos.  Biological Conservation 81: 161-177. 

ii. Green, G.I., D.J. Mattson & J.M. Peek  (1997). Spring feeding on ungulate carcasses by grizzly bears in Yellowstone National Park.  Journal of Wildlife Management 61: 1040-1055.
iii. Craighead, J.J., J.S. Sumner & J.A. Mitchell  (1995).  

The Grizzly Bear of Yellowstone: Their Ecology in the Yellowstone Ecosystem, 1959—1992.  Island Press, Washington, D.C.


11) Consumption of whitebark pine seeds (Pinus albicaulis): Black and grizzly bears farther north (e.g., the east front of the Montana Rockies on up into the Alberta Rockies) are also known to consume whitebark pine seeds, but no population of bears has as intensively used this food resource as have grizzlies in the Yellowstone region. Yellowstone was also the first place where the unique dependence of bears on red squirrels for access to seeds in cones that the squirrels had cached in middens was documented. Consumption of current-year crops typically starts in August and can resume again during early summer of the following year if the cone/seed crop was large enough.


i. Mattson, D.J., K.C. Kendell & D.P. Reinhart  (2001).  Whitebark pine, grizzly bears and red squirrels. Pages 121-136 in D.F. Tomback, S.F. Arno, & R.E. Keane, editors.  Whitebark Pine Communities: Ecology and Restoration. Island Press, Washington, D.C.  
ii. Podruzny. S.R., D.P. Reinhart & D.J. Mattson  (1999).  Fire, red squirrels, whitebark pine, and Yellowstone grizzly bears.  Ursus 11: 131-138.
iii. Mattson, D.J., & D.P. Reinhart  (1997).  Excavation of red squirrel middens by Yellowstone grizzly bears. 
Journal of Applied Ecology 34: 926-940.
iv. Mattson, D.J., & D.P. Reinhart  (1994).  Bear use of whitebark pine seeds in North America. Pages 212-220 in W.C. Schmidt & F.-K. Holtmeier, compilers.  Proceedings — International Workshop on Subalpine Stone Pines and Their Environment: The Status of Our Knowledge.  U.S. Forest Service General Technical Report INT-GTR-309.  
v. Mattson, D.J., & C. Jonkel  (1990).  Stone pines and bears.  Pages 223-236 in W.C. Schmidt & K.J. McDonald, compilers.  Proceedings — Symposium on Whitebark Pine Ecosystems: Ecology and Management of a High-Mountain Resource.  U.S. Forest Service General Technical Report INT-270.


12) Consumption of army cutworm moths (Euxoa auxiliaris): Bears farther north in Glacier NP and at a few sites in New Mexico are known to consume army cutworm moths, but none to the extent that grizzlies do in the Absaroka Range of the Yellowstone region. Grizzlies here are known to use >35 alpine sites to consume moths during July-September, all at elevations >10,000' and all on the east side of the ecosystem.


i. French, S.P., M.G. French & R.R. Knight  (1994).  Grizzly bear use of army cutworm moths in the Yellowstone ecosystem. International Conference of Bear Research & Management 9: 389-399.
ii. Mattson, D.J., C.M. Gillin, S.A. Benson & R.R. Knight  (1991).  Bear feeding activity at alpine insect aggregation sites in the Yellowstone ecosystem.  Canadian Journal of Zoology 69: 430-2435.


13) Consumption of spawning cutthroat trout (Oncorhynchus clarki) and Utah suckers (Catostomus ardens): Grizzlies consume spawning salmonids in many coastal regions, but none of the interior grizzly bear populations are known to have consumed spawning trout (and suckers) to the extent that Yellowstone bears did. Spawners were consumed during May-July almost exclusively in streams tributary to Yellowstone Lake. Consumption of spawning suckers occurred in a stream tributary to Heart Lake (Witch Creek). Consumption of spawning trout by grizzlies is also known from other streams in the Yellowstone region.


i. Haroldson, M.A., K.A. Gunther, D.P. Reinhart, S.R. Podruzny, C. Cegelski, L. Waits, T. Wyman & J. Smith  (2005).  Changing number of spawning cutthroat trout in tributary streams of Yellowstone Lake and estimates of grizzly bear visiting streams from DNA. Ursus 16: 167-180.
ii. Mattson, D.J., & D.P. Reinhart  (1995).  Influences of cutthroat trout (Oncorhynchus clarki) on behaviour and reproduction of Yellowstone grizzly bears (Ursus arctos), 1975-1989.  Canadian Journal of Zoology 73: 2072-2079.
iii. Reinhart, D.P., & D.J. Mattson  (1990).  Bear use of cutthroat trout spawning streams in Yellowstone National Park.  International Conference on Bear Research & Management 8: 343-350.


14) Consumption of thistle stalks/stems (Circium scariosum): Grizzlies in Yellowstone are the only population known to consume the stalks of this one species of thistle (they also occasionally dig its' root). Consumption occurs after careful removal of the spiny leaves and flower head. At peak succulence this thistle can taste as good as the best store-bought celery. Almost all consumption occurs in moist meadows at mid to high elevations.

Mattson, D.J.  (2000).  Causes and Consequences of Dietary Differences Among Yellowstone Grizzly Bears (Ursus arctos) 

Ph.D. Dissertation, University of Idaho, Moscow, ID.  173 pp.


There are other foods and feeding behaviors that contribute to making Yellowstone’s grizzly bears and their habitat truly unique worldwide. Yellowstone grizzly bears are a natural treasure in their own right, as a repository of singular behaviors, and as a living museum of behaviors once widespread but now lost everywhere else. Given this rich trove of biodiversity, it is intriguing, even dismaying, that few advocates of the Yellowstone grizzly bear and no agency scientists or managers feature this aspect of Yellowstone bears in conservation efforts, or seem to understand the true consequences when unique foods and behaviors are lost—as with cutthroat trout and whitebark pine during the last two decades. 

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