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Project Accomplishments

Development of Methods to Control Rodent Populations and Damage with an Emphasis on Invasive House Mice and Native Voles

PROJECT GOAL: Develop methods to reduce invasive and native rodent damage with both lethal and nonlethal approaches and reduce environmental and nontarget animal hazards with a primary emphasis on invasive house mice and native voles.

Project Accomplishments 2010

Molecular Genetics of Roof Rats in the U.S. Virgin Islands—National Wildlife Research Center (NWRC) scientists conducted a genetic analysis of tissues from ship rats ( Rattus rattus) captured on Congo Cay in the U.S. Virgin Islands and three other nearby islands to determine if the rats had survived an eradication effort in 2006 or re-invaded the area from neighboring islands. Analysis suggests that there was a single invasion, or if there were multiple invasions, that the rats came from a single source with limited genetic diversity. Model simulations indicated that, with no immigration among islands, it would require 100 rats to give rise to the present level of genetic differentiation between the islands. With immigration, 500 generations would be required.

These results indicate that the rats had not invaded from neighboring islands, but rather had survived the eradication effort. This information is useful for wildlife managers, as it indicates that future rat eradication efforts should consider the islands as independent eradication units.

Behavior of Invasive House Mouse—House mice ( Mus musculus) pose a threat to the native flora and fauna of islands and can cause significant damage wherever they have been introduced. Methods used to eradicate high-density invasive rodent populations such as house mice might not be appropriate for intercepting the rodents at lower densities. A better understanding of the behavior of house mice immediately after they are introduced to a novel environment would help wildlife managers develop effective biosecurity techniques to protect against new invasions.

To help address this problem, NWRC researchers conducted a controlled laboratory experiment that simulated an invasion by wild house mice into a novel environment. The researchers quantified and compared the immediate (within 15 minutes) behaviors of house mice by testing various odors and other attractants (e.g., foods and other mice, shelter, water, and a control). Results showed that mice presented with novel stimuli most commonly sought shelter in a den box. Secondarily, the mice were interested in food scents, particularly cheese, bacon grease, almond extract, and peanut butter. Females investigated male urine and feces odors more often than males investigated female odors.

Based on these findings, the researchers surmised that a secure den box that includes certain food and mice odors might entice and hold mice in a restricted area for a short duration in a novel environment. If done properly, this arrangement could be utilized for early detection and response to newly-invading house mice.

Effects of Vitamin K-Rich Plants on Anticoagulants in Voles—Voles ( Microtus spp.) can cause significant losses to vegetable production in California. To reduce vole populations and damage, growers typically rely on anticoagulant rodenticide baits. However, in recent years, the efficacy of those rodenticides has been decreasing. One hypothesis suggests that voles foraging on green leafy plants consume high levels of vitamin K, the antidote to anticoagulants. In a recent study, NWRC scientists tested this hypothesis by feeding voles diets that were high in vitamin K (in green leafy plants commonly grown in California) prior to exposing them to either a chlorophacinone rodenticide bait, a diphacinone rodenticide bait, or a control bait (rodent chow). Mortality was 100% in voles fed the chlorophacinone bait and 60% in those fed the diphacinone bait. These results indicate that plants rich in vitamin K may counteract the effects of diphacinone but not chlorophacinone in voles.

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