Biologists of the Denver Wildlife Research Center are currently investigating ways of managing mountain beaver (Aplodontia rufa) populations and are developing methods for alleviating mountain beaver damage to conifer trees being grown for timber in the Pacific Northwest. Studies initiated in I 986 indicated that aversive conditioning with Big Game Repellent Powder (BGR-P) dusted on cull Douglas-fir (Pseudotsuga menziesii) seedlings placed in burrows significantly reduced mountain beaver damage to planted seedlings treated with BGR-P and to untreated seedlings. Trials also showed that strychnine-sword fem (Polystichum munitum) baits prepared with a 4.9% (active) strychnine paste concentrate (SLN Reg. No. ID-870003) are very effective and selective for mountain beaver control. Other subjects discussed include results of several probes with toxic baits and phosphine gas, trials with a drug and a wetting agent to induce hypothermia, destruction of underground nests to prevent reinvasion, and mountain beaver behavior associated with controlling damage.

Principal methods being used to alleviate browsing damage to Douglas-fir (Pseudotsuga menziesii) seedlings by black-tailed deer (Odocoileus hemionus columbianus) in the Pacific Northwest are animal repellents applied to foliage and plastic mesh cylinders around individual seedlings. As an alternate method, we demonstrated that prompt establishment of highly palatable native forbs reduced summer browsing on planted seedlings to the point that black-tailed deer were no longer a factor limiting Douglas-fir regeneration. We believe that establishing native forbs is a sound ecological approach to deer-reforestation problems; furthermore, it should have wide utility because it integrates forest- and wildlife-management objectives by promoting prompt regeneration of conifers and enhancing wildlife habitat.

In a program to evaluate repellents for protecting Douglas-fir (Pseudotsuga menziesii) seedlings from browsing by black-tailed deer (Odocoileus hemionus columbianus), a preference-testing system was developed to supplement preliminary pen tests. The system uses an apparatus that presents individual test deer with a choice between two foods (usually feed pellets treated with a candidate repellent or a marginally palatable standard). The two foods are presented, in alternating positions, only long enough for the deer to make a choice; results are recorded in terms of percent choices made for the candidate repellent, or percent consumption. Tests thus far with a number of candidate repellents, including several chemical fractions derived from putrefied fish, have generally given clear-cut results, and the system appears very promising for this kind of evaluation. Although semi-tame deer and an experienced operator are required, the system uses very small amounts of candidate repellents, produces evaluations on a material in 1 to 2 days, can be used year-round, and permits observations of deer behavior during the choice process.

Economic losses caused by herbivores and other species that inflict damage by browsing or gnawing are substantial. Because lethal approaches to damage reduction are not always practical or desirable, there is an increase in interest in the development of alternative, non-lethal technologies. Repellents may provide a feasible alternative. Here, we present recent studies of three repellent types: 1) anthranilate derivatives (e.g., methyl anthranilate), 2) predator scents (e.g., coyote urine), and 3) bittering agents (e.g., denatonium saccharide). Anthranilate derivatives and predator odors both appear to be promising repellents. Avoidance of the former substances is based on irritant volatiles, and anthranilates may be especially beneficial when the aim is to prevent gnawing damage. Predator odors may be most applicable for protection of vegetation. The effectiveness of these substances appear to be based on the presence of highly volatile, light molecular weight sulfur compounds. Unlike anthranilates or predator odors, bitter substances are largely ineffective as repellents for herbivores.

Laboratory tests, field telemetry trials, and actual use field efficacy evaluations showed that a 0.5% strychnine alkaloid steam-rolled oat-groat hand-bait formulation (EPA Reg. No. 56228-20) with molasses, salt, glycerine, and soda was effective in controlling northern pocket gophers (Thomomys talpoides). Baits retaining at least 0.5% strychnine (w/w) were as effective (>95% control) as baits with 0.75% and 1.0% strychnine in field telemetry hand-baiting trials as well as operational hand-baiting and burrow-builder baiting field tests in forest habitat. Data indicated that the 0.5% strychnine hand bait (molasses formulation) should be reregistered and would be a good substitute for the 0.5% strychnine-Rhoplex bait (EPA Reg. No. 5622812) currently registered for burrow builder use for pocket gopher control. Both the retention of strychnine on bait and use of a highly palatable top quality bait carrier were two important factors affecting efficacy of the bait.