Digging deep: hoary marmots (Marmota caligata) use refuge burrows excavated by grizzly bears (Ursus arctos)

Abstract

Hoary marmots (Marmota caligata) dig burrows in alpine meadows rich in forage as ready refuge from potential predators. Refuge burrows enable hoary marmots to engage in risk-sensitive foraging when they are away from more secure resting burrows on talus slopes. Grizzly bears (Ursus arctos) commonly excavate refuge burrows while hunting marmots, substantially changing the physical characteristics of the burrow by removing earthen material. However, it is not known if marmots continue to use excavated burrows as refuge. We opportunistically inspected 22 burrows excavated by grizzly bears for use by marmots at two sites in northwestern Canada. We found marmot feces at 10 of 22 excavated burrows, indicating that marmots continued to use these burrows after they were excavated by bears. While marmots may dig several refuge burrows in alpine meadows, and bears may substantially modify them while hunting marmots, our observations indicate that some excavated burrows retain value for foraging marmots. However, the extent of their utility is unknown. We postulate several reasons why hoary marmots may use excavated burrows and suggest avenues for further research.