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Development of an Apparent Conditioned Taste Aversion in
Predators Fed Estrogen in Eggs


College of Natural Resources, University of Wisconsin-Stevens Point,
Stevens Point, WI 54481; Department of Biological Sciences, Northern
Illinois University, DeKalb, IL 60115; Bureau of Research, Wisconsin
Department of Natural Resources, 3911 Fish Hatchery Road, Madison,
WI 53711

Nesting success for waterfowl and other upland nesting species is reported to be below replacement levels in many studies. Predation is the primary factor identified for this low productivity. Conditioned taste aversion (CTA) has been proposed as a possible way to reduce nest predation. We conducted an evaluation of ethinyl estradiol on red fox (Vulpes fulva), opossum (Didelphis marsupialis), raccoon (Procyon lotor), and striped skunk (Mephitis mephitis) in captivity. Animals were individually caged and were fed eggs and a commercial pellet ration ad librum prior to treatment. Randomly selected animals were fed eggs injected with 10 to 120 mg of 17 alpha ethinyl estradiol mixed with flour to prevent enzymatic breakdown. Red fox, opossum, and raccoon, but not striped skunks, developed an apparent conditioned taste aversion because they avoided or consumed fewer untreated eggs after treatment with estrogen. There was substantial variability in dose response and length of time CTAs were observed between both species and between individuals within species.
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