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.

Non‐lethal control of wildlife: using chemical repellents as feeding deterrents for the European badger Meles meles

“…Individuals avoided ziram baits at a distance for the last 12–22 treatment nights (24–44 trial nights), and sampled them only very rarely. After eating all other baits, badgers often returned to walk around at the site, apparently ignoring the intact ziram baits (similar behaviour has been observed among racoons with CTA towards eggs; Semel & Nicolaus 1992). Our badgers stopped eating baits abruptly following full consumption, a feature characteristic of CTA (Dimmick & Nicolaus 1990).…”

“…This suggests that there was no significant social transmission of CTA. Although social communication about foods has not been studied in badgers, research on racoons and Norway rats Rattus norvegicus indicates that CTA is not socially transmitted to naive individuals (Semel & Nicolaus 1992; Galef 1997).…”

“…Nicolaus and co-authors, have performed a number of studies testing CTAs as wildlife management tools for the protection of untreated foods from damage by free-ranging racoons, mongooses Herpestes auropunctatus and guilds of mammalian predators including American badgers Taxidea taxus. In these studies, animals avoided untreated foods at a distance, probably through secondorder conditioning or potentiation (Nicolaus, Hoffman & Gustavson 1982;Nicolaus & Nellis 1987;Nicolaus et al 1989c;Semel & Nicolaus 1992). Second-order conditioning is a two-stage process: first, the taste of food becomes aversive when paired with illness; secondly, non-taste cues become associated with the now aversive taste, and themselves inhibit approach or attack (Gustavson et al 1974).…”

“…A few notable exceptions have demonstrated the utility of studying detailed behavioural responses among individually known, free‐ranging animals in determining the effect of a repellent (e.g. racoons Procyon lotor , Nicolaus, Hoffman & Gustavson 1982; Semel & Nicolaus 1992; red‐winged blackbirds Agelaius phoenicus , Nicolaus & Lee 1999; black bears Ursus americanus , Ternent & Garshelis 1999). Our work adds a further level of detail to the study of behaviour aversion (e.g.…”

Low Acute Exposure to Organophosphate Produces Long-Term Changes in Bird Feeding Behavior

“…There were no special conditions of which we are aware contributing to the results we obtained. Rather, continuing avoidance of untainted referent foods by predators that fail to discriminate between tainted and untainted prey is typical of what one sees when CTA is experimentally produced under field conditions (Nicolaus et al 1982, Nicolaus et al 1983, Nicolaus 1987, Nicolaus et al 1989b, c, Dimmick and Nicolaus 1990, Semel and Nicolaus 1992. Continuing avoidance of untainted prey, however, is not observed when predators are provided with a clear basis for discriminating between tainted and safe prey , Forthman-Quick 1985, Gustavson and Nicolaus 1987, Nicolaus and Nellis 1987, Nicolaus et al 1989c, Avery and Decker 1994, Ratnaswamy et al 1997.…”