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Potential flotation devices for aerial delivery of baits to brown treesnakes

  • Author(s): Savarie, Peter J.
  • Tope, Kenneth L.
  • et al.
Abstract

Brown treesnakes are exotic invasive predators that have extirpated native forest birds and caused drastic reductions of lizards on Guam. Operational management control methods to contain the snake on Guam include the use of live traps, hand capture from fences, and canine detection. Live traps are also used to depopulate small forest plots. Toxicants offer an additional means for reducing snake populations on small plots. Polyvinyl chloride (PVC) plastic pipe bait stations containing dead neonatal mice (DNM) treated with 80 mg acetaminophen are placed about 1.5 m above the ground in vegetation to reduce exposure to terrestrial scavengers such as toads, crabs, and feral pigs. Live traps or bait stations are not practical to use in remote, large-scale areas of forest but aerial delivery of baits may have application. Small plastic parachutes have been used for entangling DNM in forest canopy but parachutes are relatively expensive and cumbersome to use. Inconveniences can be tolerated when only a small number are deployed. But it is anticipated that several thousand baits may be delivered per drop, and inconveniences must be kept to a minimum to maintain an efficient aerial drop system. We therefore evaluated 5 types of flotation materials dropped by helicopter, using DNM implanted with radio transmitters to record landing site (canopy or ground) and bait consumption by snakes and non-target animals. The types of material and percentage of baits that became entangled in the canopy were: paper ring – 39%, paper drinking cup – 50%, excelsior (wood shavings) and burlap – each 56%, and commercial paper food cup – 60%. For all devices, bait consumption by snakes ranged from 19-50% and bait consumption by non-target toads and crabs ranged from 0 - 11%. Commercial food cups were the most convenient material to use because they could be nested together prior to deployment.

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