Dan L. Campbell

Why are predator urines aversive to prey

Predator odors often repel prey species. In the present experiments, we investigated whether changes in the diet of a predator, the coyote (Canis latrans) would affect the repellency of its urine. Furthermore, because predator odors have a high sulfur content, reflecting large amounts of meat in the diet, we investigated the contribution of sulfurous odors to repellency. Our results were consistent with the hypothesis that diet composition and sulfurous metabolites of meat digestion are important for the repellency of predator odors to potential prey.

Effects of Predator Odors on Feeding in the Mountain Beaver ( Aplodontia rufa )

Consumption of food by Aplodontia rufa from bowls scented with control odors, secretion from anal glands of minks ( Mustela vison ) or urine from minks, bobcats ( Felis rufus ) and coyotes ( Canis latrans ) was studied. In two-choice control tests, subjects indiscriminately consumed apple from unscented bowls and from bowls scented with urine from an unfamiliar herbivore ( Cavia porcellus ), or with butyric acid. During two-choice tests offering apple from bowls scented with secretion from anal glands of minks and from bowls scented with butyric acid, significantly less apple was consumed from bowls containing mink scent. In two-choice tests in which apple was offered from bowls scented with urine from either mink, bobcat, coyote, or domestic dog, all predator urines reduced feeding. Habituation was studied by measuring consumption of dry pellets during continuous exposure to coyote urine for 5 days. Significantly less chow was consumed from bowls scented with coyote urine than from control bowls, indicating a lack of habituation to the predator scent. We conclude that predator scents act as natural repellents. The responsiveness to scents from several sympatric predators as well as from domestic dogs suggest an innate reaction to a signal, which is common to carnivores. The utility of predator scents in the control of browsing damage by mountain beavers should be explored.

Potential repellents to prevent mountain beaver damage

Mountain beaver (Aplodontia rufa) damage to trees in the Pacific Northwest is economically serious. At present, few strategies are available to control damage, and new chemical repellents are being sought. Samples of two preferred plants, Douglas fir (Pseudotsuga menziesii) and salal (Galtheria shallon), were treated with mink urine, coyote urine, o-aminoacetophenone, or denatonium benzoate and presented to mountain beavers. All treatments reduced clipping (p < 0.05) of salal, but mink and coyote urines were most effective. Mink and coyote urines were the only treatments to significantly reduce clipping (p < 0.05) of Douglas fir.

Feeding Responses to Predator-Based Repellents in the Mountain Beaver ( Aplodontia rufa )

Predator odors have potential as feeding repellents for mammalian herbi- vores, including Aplodontia rufa, the mountain beaver. However, the repellency of major chemical constituents of natural predator scents for this species has not been evaluated. In this study, the effects of several synthetic sulfur compounds from predator scents on feeding by mountain beavers were assessed and compared to the effects of coyote (Canis latrans) urine. Retrieval of food by mountain beavers from bowls scented with either coyote urine, diluted with water to different concentrations, synthetic components of predator scents, or control odorants was studied. The following synthetic compounds were tested: A3-Isopen- tenyl methyl sulfide (IMS), a compound present in urine from several canid species; 2,2 dimethylthietane (DMT), a major constituent in anal gland secretion from the mink (Mustela vison); a 1:1 mixture of 2-propylthietane (PT) and 3-propyl- 1,2-dithiolane (PDT), com- pounds occurring in anal gland secretions from the stoat (Mustela erminea) and the ferret (Mustela putorius). Habituation to PT plus PDT was studied by measuring consumption of dry pellets during continuous exposure to these compounds for 5 d. In two-choice feeding trials mountain beavers retrieved significantly more food from bowls scented with water than from bowls scented with coyote urine. Dilution of urine had no statistically significant effect on food retrieval, but repellency tended to decrease with decreasing concentration. Mountain beavers retrieved less food scented with a 1:1 mixture of PT and PDT, compared to controls. However, they rapidly habituated to this mixture. None of the other compounds caused an avoidance response. These results show that complex natural predator scents are more effective feeding repellents than some of their major volatile components alone.

Pine needle oil causes avoidance behaviors in pocket gopherGeomys bursarius

Essential oils from coniferous trees contain secondary metabolites that act as feeding deterrents for a number of herbivorous mammals. We investigated effects of pine needle oil on feeding and other behaviors of herbivorous plains pocket gophers. In experiment l, pocket gophers were offered sweet potato from single feeding stations placed in home cages of individually housed animals. Stations contained either a scent dispenser with pine needle oil or mineral oil. Subjects removed significantly less food from stations scented with pine needle oil. Experiment 2 was performed to investigate neophobic responses to odors.d-Pulegone, presented under conditions identical to those used in experiment l, did not reduce food removal compared to mineral oil. In experiment 3 pocket gophers were observed in a maze consisting of a start box connected to two goal boxes by tunnels. One goal was scented with pine needle oil, the second with mineral oil. Subjects entered goals scented with pine needle oil significantly less frequently than goals scented with mineral oil and spent less time there. They performed all recorded behaviors at lower frequencies while located in pine-scented goals. In experiment 4 animals were introduced into a maze consisting of a start box from which two soil-packed tunnels could be entered. Embedded in the soil of one tunnel was a barrier of electrical cable that had been soaked in pine needle oil, the second tunnel contained a barrier of cable soaked in mineral oil. Pocket gophers gnawed significantly less insulation from cable treated with pine needle oil than from cable treated with mineral oil. Our results show that constituents in pine needle oil are aversive to plains pocket gophers. Under natural conditions they may function as feeding deterrents. Some of the compounds may be suitable repellents for control of pocket gopher damage.

Pocket gopher reoccupation of burrow systems following population reduction

Abstract The application of rodenticide baits to pocket gopher burrows can quickly reduce gopher density on reforestation units, but the food resources and burrow systems remain intact. This, coupled with the rodents high reproductive and dispersal potentials, allows for rapid repopulation of treated sites. We monitored 73 pocket gopher activity plots in southern Oregon which had been rendered inactive with toxic baits. The plots promptly returned to active, indicating rapid reoccupation by gophers. Six months after baiting, 86% of plots were reoccupied. By one year post-baiting, 96% of plots were reoccupied. These results demonstrate the potential for rapid population recovery following rodenticide treatment and emphasize the need for an integration of other methods to avert damage to reforestation efforts for the long term.

Field trials of pocket gopher control with cholecalciferol

Abstract Cholecaliferol (Vitamin D3) was evaluated as a field rodenticide for controlling pocket gophers (Thomomys spp.) under forest and seed orchard conditions by monitoring radio-equipped pocket gophers following the application of 0.0%, 0.003%, 0.04%, 0.075% and 0.15% cholecalciferol oat baits. In one trial, the difference in mortality of the three lower concentrations was not significantly greater than the control group. In two subsequent trials with the higher concentration (0.15%), mortality between the treatments was significantly greater than in the control groups. We recommend that primary and secondary hazards of cholecaliferol to nontarget species and predators be investigated.