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In October 1995, a 12,000-acre wildlands fire on the Point Reyes peninsula in northern California burned 40 percent of the known range of the Point Reyes mountain beaver (Aplodontia rufa phaea), including most of what was believed to be prime habitat. The fire burned through thickets and revealed thousands of mountain-beaver burrow openings. This exposure enabled researchers to assess the pre-fire distribution and population size of mountain beavers within the burned area and to evaluate their survival and recovery. U.S. Geological Survey (USGS) scientist Gary M. Fellers and collaborators David Pratt (National Park Service) and Jennifer L. Griffin (consultant) recently published their findings about the fire's effects on mountain beavers in the Journal of Wildlife Management.
Mountain beavers are not true beavers but rather muskrat-size animals that live in underground burrows dug in forest openings and dense thickets. Sedentary, primitive rodents with a 5- to 6-year lifespan, mountain beavers mature in their second year and then produce two to three young each spring. Because they have primitive, inefficient kidneys, their water requirements are unusually high: they must drink a third of their body weight daily. Mountain beavers feed on various plants, including nettles, blackberry, poison oak, and coyote brush. In California, two small, geographically isolated, distinct subspecies live along the coast: the Point Reyes population and the endangered Point Arena population. More extensive populations live in the Sierra Nevada and in the Pacific Northwest.
Systematic surveys of mountain-beaver habitat at Point Reyes National Seashore had been conducted before the 1995 fire, from 1984 to 1994, and the presence of mountain beavers had been confirmed, but population size could not be determined because dense vegetation hid the burrow openings.
In the first six months after the 1995 fire, researchers surveyed burned coastal scrub to count and map burrow openings. They estimated that 5,000 mountain beavers had occupied the areas before the fire. The presence of fresh dirt outside burrow openings and photographs from remotely triggered cameras documented 19 mountain beavers that had survived the fire and the immediate post-fire period. This number represented less than 2 percent of the original population. Activity was monitored for 5 years at eight sites where mountain beavers had survived the fire and at three sites where there were no survivors. The researchers found recovery at some of the eight sites and found migration into only one of the three sites where fire had eliminated the original population. They estimate that recovery may take 15 to 20 years.
In their recent article in the Journal of Wildlife Management (v. 68, no. 3, p. 503-508), the researchers suggest that the slow recovery may be caused by shifts in plant-species composition and in the physical structure of thickets. Limited dispersal of mountain beavers between suitable sites may also retard recovery. As the vegetation becomes more suitable, an increase in mountain beavers likely will occur as a result of population growth and immigration from outside the burned area. The scientists' findings have several implications for the management of mountain beaver habitat:
The full citation of the researchers' paper is: Fellers, G.M., Pratt, David, and Griffin, J.L., 2004, Fire effects on the Point Reyes mountain beaver (Aplodontia rufa phaea) at Point Reyes National Seashore: Journal of Wildlife Management, v. 68, no. 3, p. 503-508.
in this issue:
Mountain Beaver Population Slow to Recover After Wildfire
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