Using eggs containing an irritating odor to teach mammalian predators to stop depredating eggs

Mammalian predation on eggs has reduced many avian populations below histor ic levels. Nonlethal approaches to resolve predation problems are preferred by society, but often are ineffective or too expensive. We examined whethe r mammalian predators could be taught to stop opening all eggs (treated and untreated) after the predators were preconditioned by being allowed to ope n eggs containing an irritating odor. We tested this using 29 captive coyot es (Canis latrans) and pulegone, a Volatile chemical that is irritating to coyotes. The first experiment consisted of a 1-day pretreatment when each c oyote 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 untr eated, one coated with pulegone, and one injected with putegone and then se aled in polyurethane. All coyotes ate untreated eggs during the pretreatmen t period and also ate the first pulegone-treated egg presented to them. Aft er that, coyotes gradually stopped opening and consuming eggs injected with pulegone. During the post-treatment period, coyotes resumed eating untreat ed eggs, indicating that they had developed an aversion to putegone but not to eggs. During choice tests, coyotes discriminated against pulegone-injec ted eggs and pulegone-scented eggs. This suggested that it might be possibl e 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 peri od when all eggs were injected with pulegone, Lye conducted a choice test i n which 8 nests contained untreated eggs, 4 nests contained eggs sprayed wi th pulegone, and 4 nests were spayed with pulegone but contained untreated eggs. Coyotes consumed fewer eggs from pulegone-scented nests than from uns cented 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 t hen spraying pulegone on the ground near those nests that we wish to protec t. Such an ability would be useful in multi-species colonies when we want t o protect a particular species from predation. However, pulegone is toxic t o egg embryos, so care must be taken not to allow it to contact the eggs.