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Reducing Egg Predation with Estrogen-based Conditioned
Taste Aversion

LOWELL K. NICOLAUS, JOSE' HERRERA,
AND JANIS C. NICOLAUS

Department of Biological Sciences, Northern Illinois University,
DeKalb, IL 60115-2861

During the summer of 1988, we conducted two field evaluations of 17 alpha-ethinyl estradiol as an illness-causing conditioned taste aversion (CTA) agent capable, because of its low detectability, of producing generalized avoidance of eggs among mammalian egg predators. These included: raccoons (Procyon lotor), skunks (Mephitis sp.), opossums (Didelphis virginiana), red foxes (Vulpes vulpes), badgers (Taxidea taxus) , and coyotes (Canis latrans). In the first trial, nocturnal predation upon eggs was measured at 21 independent sites along the Mississippi River border between Illinois and Iowa. During the last half of the 19-day first trial, predation on untreated central and untreated peripheral eggs at eight control sites was 96.3 and 95.8% of available eggs, respectively. By this time, predators at five lithium treatment sites had learned to discriminate between peripheral eggs with 1.5 g of illness-causing, but salty-tasting, lithium chloride and untreated central eggs, attacking 29.2% of the former and 86.3% of the latter. Predators visiting the eight estrogen sites, however, appeared not to detect the estrogen and so failed to discriminate between untreated central eggs and peripheral eggs treated with 5.6 mg of estrogen, attacking 34.0% of the untreated eggs and 54.8% of the treated eggs. In the second trial, the eight original control sites had four times as many central and peripheral eggs, and in four of these sites peripheral eggs each contained 9.5 mg of estrogen. By the last half of the 20-day period, predation on untreated central eggs and treated peripheral eggs at estrogen sites declined to 4.9% and 27.6% of that at control sites, respectively.
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