Chemical Repellents and Other Aversive Strategies in Predation Management. (Predation Management)
Mason, J. R., Shivik, J. A., Fall, M. W., Endangered Species Update
Chemical repellents and other aversive strategies are the core of non-lethal wildlife management. These strategies typically depend on irritation (pain), conditioning, or fear for their effectiveness, and none is universally successful. Thus, conditioned food aversions deter browsing and foraging by deer (Odocoileus virginianus, O. hemionus), but are less useful with predators, because killing, not consumption, is the behavior of interest. Broadly speaking, the utility of non-lethal strategies is affected by number and density of wildlife species, availability of alternative foods, palatability and novelty of treated items, and intensity of pain, sickness, or fear used to establish avoidance. Some of the most promising areas for successful predation management are those involving a combination of strategies tailored to a specific problem. For example, behavioral-contingent auditory and visual stimuli coupled with presentations of electric shock or momentary vibration (via telemetry collars) could provide an effective and unambiguous cue for withdrawal. Non-lethal methods, however, are rarely stand-alone technologies. More often, integrated strategies, involving both lethal and non-lethal methods, are required for effective predation management.
The survival or restoration of threatened and endangered species can depend on protection from predators (Witmer and Fall 1995; Witmer et al. 1996; Hecht and Nickerson 1999). Most of the relevant data for managing predation stem from research on the protection of livestock, crops, and commodities (Campbell et. al 1998; Fall and Jackson 1998). Deterring predators from prey is even more complex than protecting crops or other commodities because more is involved than food consumption (Fall 1990; Knowlton et al. 1999). Especially challenging is the development of non-lethal approaches. Demand for these strategies is increasing despite the fact that effective options remain virtually nonexistent. Repellents and other aversive techniques provide cases in point. If wildlife numbers are sufficiently high, or alternative foods are sufficiently scarce, repellents usually fail as a deterrent. Few demonstrably effective alternatives exist, and practical obstacles to the development of new materials are considerable. The present discussion will cover these topics by considering: mechanisms underlying the effectiveness of repellents and aversive agents, regulatory constraints that govern implementation of new methods, and the importance of employing multiple sensory modalities (i.e. visual and auditory cues, chemical and color cues) whenever non-lethal strategies are implemented.
Vertebrate chemical repellents are effective because they are irritating, cause sickness, or stimulate fear (Mason and Clark 1997). As a rule, these substances are most useful when they are applied directly to inert materials (e.g., prepared foods, fruits, grains, electrical wiring, irrigation hose; Werner et al. 1998). There is no good evidence that predators or other wildlife will avoid areas protected solely with border treatments. To illustrate the point, Renardine is commercially available for use with red fox (Vulpes vulpes) in the United Kingdom and is being evaluated for use with coyotes (Canis latrans) in Canada (Martin and O'Brien 2000). (Mention of trade names and manufacturers is for identification only and does not imply endorsement by the authors or the U.S. Department of Agriculture.) The substance is bone tar oil dissolved in kerosene. The label advises that it should be applied liberally to pasture borders (on fence posts, etc.) to prevent predators from entering and attacking livestock. In testing with captive coyotes in the U.S., not only did Renardine fail to prevent entries into areas, but food adulterated with the material was eaten as rapidly as unadulterated food (Zemlicka and Mason 2000). This probably reflects the fact that sulfurous compounds in bone tar oil are attractive to coyotes (see Fear below). …