Using Eggs Containing an Irritating Odor to Teach Mammalian Predators to Stop Depredating Eggs

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Wildlife Society Bulletin

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Mammalian predation on eggs has reduced many avian populations below historic levels. Nonlethal approaches to resolve predation problems are preferred by society, but often are ineffective or too expensive. We examined whether mammalian predators could be taught to stop opening all eggs (treated and untreated) after the predators were preconditioned by being allowed to open eggs containing an irritating odor. We tested this using 29 captive coyotes (Canis latrans) and pulegone, a Volatile chemical that is irritating to coyotes. The first experiment consisted of a 1-day pretreatment when each coyote was given an untreated egg, a 5-day treatment period when each coyote was given daily an egg injected with pulegone, and a 1-day post-treatment period when each coyote was given an untreated egg. This was followed by a 4-day choice test during which each coyote was given 3 eggs daily: one untreated, one coated with pulegone, and one injected with putegone and then sealed in polyurethane. All coyotes ate untreated eggs during the pretreatment period and also ate the first pulegone-treated egg presented to them. After that, coyotes gradually stopped opening and consuming eggs injected with pulegone. During the post-treatment period, coyotes resumed eating untreated eggs, indicating that they had developed an aversion to putegone but not to eggs. During choice tests, coyotes discriminated against pulegone-injected eggs and pulegone-scented eggs. This suggested that it might be possible to deceive predators into avoiding untreated eggs by spraying nests with pulegone. We tested this by creating a simulated nesting colony consisting of 16 nests in a field, each containing one egg. Following a treatment period when all eggs were injected with pulegone, Lye conducted a choice test in which 8 nests contained untreated eggs, 4 nests contained eggs sprayed with pulegone, and 4 nests were spayed with pulegone but contained untreated eggs. Coyotes consumed fewer eggs from pulegone-scented nests than from unscented nests. These experiments indicate that it may be possible to deflect predation in an avian nesting colony away from specific nests by exposing local predators to pulegone-injected eggs prior to the nesting season and then spraying pulegone on the ground near those nests that we wish to protect. Such an ability would be useful in multi-species colonies when we want to protect a particular species from predation. However, pulegone is toxic to egg embryos, so care must be taken not to allow it to contact the eggs.

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