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Woodchucks (Marmota monax) and meadow voles (Microtus pennsylvanicus) can be serious pests in orchards where they damage young fruit trees by gnawing on main stems. Previous work indicated that topical application of bobcat (Lynx rufus) urine to apple trees could reduce woodchuck damage by an average of 98%. Here, we report on field trials designed to determine whether various fractions of bobcat urine could achieve comparable reductions in gnawing activity. Trials with smooth sumac (Rhus glabra) resulted in an average reduction in gnawing over a 4-week period, relative to controls, of 86% for undiluted urine, 56% for a methanol extract of urine, and 25% for a solution of 5 nitrogen-containing compounds (indole, phenylacetamide, 1-methylhydantoin, 2,6-dimethylpyrazine, 6-valerolactam) in the approximate concentrations they were found in urine. Trials with apple seedlings and cuttings resulted in an average reduction in gnawing over a period of 2-3 weeks, relative to controls, of 90% for undiluted urine, 49% for a methylene chloride extract of urine, 34% for a solution containing a single sulfur-containing compound extracted from urine (3-mercapto-3-methy l-butanol) , and 30 % when this compound was mixed with three additional sulfur volatiles from urine. Reductions due to the nitrogen- and sulfur-containing fractions were not significant. We also conducted laboratory trials in which we recorded the amount of time meadow voles spent in treated versus untreated halves of an arena. Preliminary trials indicated strong aversions (P<0.01) to areas containing bobcat, red fox (Vulpes vulpes), or coyote (Canis latrans) urine, and no aversion (P = 0.56) to woodchuck urine. In subsequent trials, we tested various fractions of bobcat urine and found that the methylene chloride extract and solutions containing either 3-mercapto-3-methyl-butanol, P-mercaptoethanol, or thiophenol caused significant aversions, but the mixture of five nitrogen-containing compounds did not. Woodchucks and meadow voles respond aversively to predator urine, but we were unable to identify fractions of bobcat urine capable of eliciting aversions comparable in magnitude to those achieved with undiluted urine.