A preference-testing system for evaluating repellents for black-tailed deer

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.