Grizzly bears intentionally ingest earth, which may serve several different functions. In a famous quote about the food habits of the grizzly, naturalist John Muir states that these bears “eat everything but granite.” It turns out that Muir’s statement is not quite right, as while they have not been documented to eat rocks, they will eat earth! Some of the soil found in grizzly scat is not doubt ingested unintentionally along with their normal foods, like roots and ground squirrels. But grizzlies also intentionally eat soil and river sediment.
There are a few anecdotal accounts of brown bears diving down in the river ways in which they fish to take mouthfuls of mud from the river bottom. It has been suggested that they do this to clean their alimentary tracts of internal parasites. At Katmai National Park, we found brown bear scat that was comprised of fine sediment. The fecal material also contained numerous worms (I cannot be sure of the identification of the parasites involved, but they looked like a type of nematode).
In Yellowstone National Park, Mattson et al. (1999a) found 12 sites where grizzlies consume soil and found earth in some scat samples. These areas were free of vegetation due to thermal activity. Geophagy was most common between March and May and again from August to October – these correspond to times when ungulate and mushroom eating was also common. The researchers concluded the soil consumption may have several functions. Like ungulates, grizzlies may eat earth to detoxify secondary compounds present in the foliage they consume and to supplement their diet with potassium. In the areas where grizzlies ingested soil, the earth has very high in potassium, magnesium and sulphur. The authors also suggest that that by consuming these soils, the bears may prevent diarrhea by helping to get rid of some parasites and bacteria in the alimentary tract.
References:
Mattson, D.J., G.I. Green and R. Swalley. 1999. Geophagy by Yellowstone grizzly bears.
Ursus 11:109-116.
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