the parasites of the mountain beaver is the largest flea known, Hystrichopsylla schefferi. Females of this flea can be long. Mountain beavers are considered pests in areas of the Pacific Northwest because of the extensive damage they cause to forest trees due to basal-grinding (removal of bark), branch cutting, or clipping small sapling and seedlings. This damage often poses a problem for forest management and reforestation when smaller seedlings are buried or uprooted during mountain beaver feeding and can result in tree deformities, growth suppression, and mortality. The United States Forest Service has maintained a program to exterminate the mountain beaver due to beavers causing economic damage to commercial reforestation. Damage control measures taken to protect forest trees by controlling the mountain beaver population include trapping, placing toxic baits, and placing physical barriers (e.g. plastic mesh tubes) around the base of an individual tree. Breeding The breeding season is between January and March, with two or three young born February to April. The ovulation period lasts a few weeks and gestation lasts for a month. The young are born hairless, pink, and blind. They are weaned at 6 to 8 weeks and leave the burrow soon after. Lifespans are 5 to 10 years – fairly long for rodents. They are not social, though home ranges can overlap. Status and conservation The IUCN lists the mountain beaver as a species of least concern. However, one subspecies, the Point Arena mountain beaver (A. r. nigra) of California, is considered endangered by the U.S. Fish and Wildlife Service, and Critically Imperiled by NatureServe. Originally listed in 1991, the Point Arena mountain beaver is distinguished by its black colouration and by characteristic body proportions, including a smaller overall size. The principal threat to this subspecies is habitat loss and fragmentation; its remaining range comprises a disjunct region of 24 square miles in western Mendocino County. Notes References Adkins, R. M. E. L. Gelke, D. Rowe, and R. L. Honeycutt. 2001. Molecular phylogeny and divergence time estimates for major rodent groups: Evidence from multiple genes. Molecular Biology and Evolution, 18:777–791. McKenna, Malcolm C., and Bell, Susan K. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp. Nowak, R. M. 1999. Walker's Mammals of the World, Vol. 2. Johns Hopkins University Press, London. External links Fauna of the Sierra Nevada (United States) Mammals of Canada Mammals of the United States