Management of Predator Populations with Antifertility AgentsLaboratory Tests on the Effectiveness of Prolin Mouse Tubes

The search for methods, other than lethal techniques, for controlling predatory animals causing economic losses to the livestock industry prompted investigation of antifertility agents to suppress reproduction. Diethylstilbestrol was selected for initial trials because of its demonstrated antifertility effect on rabbits, mink (Mustela vison), dogs, and cattle. In penned tests with stilbestrol, pregnancy was terminated in six coyotes (Canis latrans) fed a single 100-mg oral dose dissolved in tallow. A subsequent field trial was conducted in New Mexico on 20 townships, March 5-15, 1963. Five thousand (100 mg stilbestrol in ½ ounce of tallow) drop baits were placed wherever coyote sign was found. After a delay of 3 weeks to allow the drug to take effect, a collection of female tracts from the treated area and a reference area 25 miles away was made to measure and compare reproductive success. Of the 20 females in reproductive condition recovered from the treated area, only 4 had viable embryos, while reproduction was blocked in 16 specimens by failure of implantation or resorption of embryos. All of the 13 females in reproductive condition from the reference area would have produced pups as evidenced by viable embryos. Future tests are scheduled to determine effects on other species and to confirm results on coyotes under a variety of field conditions.The Prolin mouse tube is an expendable weather-resistant cardboard bait station. The inner surface of the tube is lined with approximately 1 ounce (28.4 g) of grain treated with 0.05 percent Prolin (anticoagulent rodenticide), affixed with an edible glue. The tube was designed to control meadow mice (Microtus) in orchards. Effectiveness (acceptability and lethality) of the tubes was determined by laboratory and pen tests for eight species of small California rodents. Of the mixture of grains within the tubes, the mice preferred oats and wheat to corn.