Aerial delivery of baits to brown treesnakes

The exotic brown treesnake (Boiga irregularis) has been implicated in the extermination of endemic species from Guam, and fears that it will be transported elsewhere have resulted in an intensive trapping and containment program. Current management methods do not depopulate large areas, a presumed prerequisite for the effective reintroduction of endangered native species, and logistically tenable techniques for removing snakes from remote forests are needed. Bait stations containing dead neonatal mice (Mus musculus) implanted with acetaminophen have been effective for depopulating areas of brown treesnakes, but a bait delivery system for effective use of toxicants on a large scale and in remote areas has yet to be developed, and the selectivity of air-dropped baits requires assessment. We developed and tested aerial delivery methods of distributing baits in forest canopy on Guam by implanting baits with radiotransmitters. We recorded bait uptake by snakes and other species and measured morphology and movements of snakes that consumed baits. Bait take by snakes was high (63%) using parachuted baits designed to entangle in forest canopy, and snakes moved 1-70 m after consuming baits. Snakes that consumed baits were of similar size, weight, and body condition to snakes captured in traps on the drop areas. Implanting transmitters in carcass baits was a useful method for monitoring brown treesnake movement for 5-11 days post-consumption.