Estrogen-Based Aversion to Eggs Among Free-Ranging Raccoons.

Abstract

Nightly video records of uniquely marked free-ranging raccoons (Procyon lotor) established the events leading to and resulting from estrogen-induced conditioned taste aversion (CTA) to eggs. Observations of animals voluntarily consuming eggs indicated that: (1) some raccoons in the population were more active egg predators than were others and so were the most likely to be treated; (2) a few eggs injected with 30 mg of estrogen were less effective in inducing egg avoidance than were larger numbers of eggs treated with only 10 mg of estrogen; (3) CTA to eggs became well established even though raccoons had become familiar with eggs at the feeding site; (4) treated males tended to abandon egg consumption abruptly, but females tended to sample eggs for a short time before they, too, avoided them at a distance; (5) CTA was not location specific, persisted when surrounding scent cues changed, and failed to extinguish among treated raccoons that were present while untreated individuals consumed untreated eggs freely during the lengthy post-test period; and (6) treated females that avoid eggs may deny their offspring the opportunity to become familiar with egg prey. Observations of egg consumption in the second year of study provided evidence of a prolonged CTA effect in treated animals. Our results enable us to more fully describe a potential non-lethal technology for controlling predation on the eggs of waterfowl or endangered and threatened species.