Brown Treesnake Research at NWRC
Project Accomplishments 2010
Excluding Nontarget Species from BTS Bait Stations—Bait stations with toxic baits are a major tool in efforts to eradicate the invasive BTS (Boiga irregularis) on Guam. To reduce the hazard of nontarget animals getting into the bait stations, National Wildlife Research Center (NWRC) researchers evaluated the efficacy of three bait station designs (horizontal pipe, pipe angled downward at 45 degrees, pipe angled downward at 60 degrees) placed on three commonly used station support structures (vegetation, chain-linked fence, rebar tripod) to exclude nonnative rats (roof rat: Rattus rattus; Norway rat: Rattus norvegicus; Polynesian rat: Rattus exulans) and native coconut crabs ( Birgus latro).
Because the BTS is primarily arboreal, bait stations are typically placed approximately 1.3 meters above the ground to facilitate access by snakes and limit access by terrestrial non-target species. In laboratory studies simulating bait station placement commonly used in the field (approximately 1 meter above ground level), roof and Norway rats were equally able to enter bait stations placed on all three station support structures; Polynesian rats rarely entered any of the elevated stations. However, the ability to access only the entrances of stations (but not the interior of the stations, where the bait was placed) when on support structures was extremely high for roof rats and appreciable for the other rat species, including Polynesians. The horizontal pipe station design, when placed on a chain-link fence, had the highest probability of access by all rodent species. The two, downward-angled station designs, when placed in simulated vegetation, had the lowest probabilities of access by rats. Coconut crabs accessed station entrances readily, but never entered the interiors where the bait was.
Based on these results, the researchers recommend the suspension of either of the downward-angled station designs from vegetation wherever possible in areas where non-target species are a concern.