U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version

June 2004


Published by the Proc. 21st Vertebr. Pest Conf. (R.M. Timm and W.P. Gorenzel, Eds). Published at Univ. of Calif., Davis. 2004. Pp. 158-162. Permission to use.


The mountain beaver is a fossorial rodent species endemic to the Pacific Northwest and portions of California. This herbivore is managed as a pest species because of the impact it has on newly planted Douglas-fir seedlings. Currently, managers are limited to trapping for population control; however, in Washington trapping has been further curtailed by anti-trapping legislation. Presently there are no registered underground toxicants for mountain beaver control. We have documented the efficacy of chlorophacinone, presented in daily doses, as a possible alternative for mountain beaver control. Daily baiting would be unreasonable and costly alternative for timber managers, so we conducted a series of tests to determine if a single or double baiting was efficacious. In addition, we tested the caching behavior of the mountain beaver when offered bags of oats. This behavior may help reduce impacts to non-target species as well reduce environmental exposure and degradation. Mountain beaver readily cached bags of chlorophacinone within their artificial burrows, and efficacy of a one-lime and two-time dose was 100%. We determined that even with the highest chlorophacinone residuals (0.354 ppm) that the risk quotient for mink and red-tailed hawk was exactly at the level of concern that EPA recognizes for endangered and threatened species.