National Wildlife Research Center NWRC) |
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Brown Treesnake Research at NWRC
Project Accomplishments 2008
Brown treesnakes (BTS) were accidentally introduced to Guam in the late 1940s or early 1950s and have caused extensive economic and ecological damage to the island. In just half a century, the BTS has exterminated most of Guam’s native forest birds and greatly reduced its population of fruit bats and native lizards. WS actively manages BTS populations on Guam to prevent their spread to other Pacific islands, especially Hawaii. BTS research is a reimbursable funded project initiated in 1995 and was assigned as an official project under the Hilo, HI, field station in October 2007. The majority of the funding has been provided by the Department of Defense (DoD) Legacy Resource Management Program, the U.S. Department of the Interior’s Office of Insular Affairs, and WS Operations, and USFWS.
Paper Flags for Aerial Delivery of Baits to BTS—NWRC scientists continued developing a system for the aerial delivery of baits to BTS in forested areas of Guam. The overall goal of this work is to improve the delivery of acetaminophen baits to snakes in the forest canopy.
NWRC scientists attached dead neonatal mice (DNM) to commercially available, biodegradable paper flags that were deployed either by an automated–electromechanical dispenser or by hand from a helicopter on a 4–ha forest test site. They conducted six drops, three each by dispenser and hand; 28 of the 144 DNM flag-baits deployed per drop had a radio transmitter attached to the DNM for tracking purposes. Acceptance of the DNM was not a priority, and NWRC made attempts to recover all radios on the day of deployment.
The overall performance of both aerial delivery systems was successful. Eighty-five percent of the radioed DNM deployed by dispenser and 79% of the DNM deployed by hand got caught up in the canopy where they were accessible to BTS. NWRC deployed a total of 168 radioed DNM, 150 of which were recovered the same day and 18 of which were found the following day. Of these 18, snakes had consumed five DNM, and a marine toad ingested one.
NWRC identified two modifications that are needed to improve the aerial delivery system: (1) paper flags that are more resistant to water, as the current flags degraded and dropped the DNM to the ground when it rained, and (2) the use of a paper flag on each end of the streamer so that a loop is formed in the air, increasing entanglement in the canopy.
Evaluation of Alternative Baits for Brown Treesnakes—Initial bait studies done with BTS used DNM as the matrix for the oral toxicant (acetaminophen) for BTS. Although DNM are well accepted by BTS, the mice are expensive and become putrid after two to three days in the field. NWRC scientists are conducting reseasrch to develop a bait that is an effective alternative to DNM.
NWRC scientists conducted field studies in April (dry season) and August (wet season) 2007 to evaluate consumption of five baits for delivering acetaminophen to brown treesnakes on Guam. Test baits were placed in bait stations (polyvinyl chloride tubes) with a bolt secured halfway across each end to mitigate access by non-target animals. Bait stations were positioned horizontally about 1.5 m high in vegetation at 20-m intervals along the forest perimeter adjacent to roads and trails. Bait types were randomly assigned to bait stations and included DNM, dehydrated DNM, freeze-dried DNM, unadulterated beef, and beef treated with the decomposition products of uDNM that had “aged” under field conditions for 48 hours. Bait consumption for the beef treated with “aged” DNM was as high as 93%, comparable to untreated DNM. Results from both seasons suggest that decomposition odors of dead mice can be used to substantially increase BTS bait consumption of beef. NWRC will direct future studies towards the evaluation of synthetic bait matrices treated with decomposition products of “aged” DNM.
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