By Rachel Landers
The Joint Region Marianas Brown Tree Snake Eradication Program continues to combat the invasive snake species on Guam.
The brown tree snake (boiga irregularis) has disturbed the ecological balance of Guam since the 1950s, when the species first arrived stowed away in shipping materials. On the island, the tree snakes prey on various small animals including lizards, birds and bats.
"They are opportunistic feeders," said Megan Parker, a natural resources specialist with JRM. "Since they were introduced, there has been a cascading effect. They eat the birds; fewer birds means more pests and diseases and then there are no native birds to spread native seeds - that's another big impact."
Aside from birds, snakes prey on other small animals including lizards and bats. The ripple effects have been significant.
Marc Hall, the JRM conservation programs supervisor explained, "Brown tree snakes are probably the biggest limiting factor to the recovery of listed vertebrates [on Guam] – bats and birds. There are many factors that contribute to the recovery of those species, but the brown tree snakes seem to be causing the majority of the problem."
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JRM has been involved in efforts to address the invasive species for years. Partnerships between the Department of Defense and the Guam Department of Agriculture, U.S. Fish and Wildlife Services, and the U.S. Department of Agriculture (USDA) allow for interdiction and mitigation. Since 1994, interdiction programs have included traps on airfield fences and inspections conducted by specially trained brown tree snake detection dogs. The long-running programs ensure snakes do not stow away on military equipment or shipping containers leaving the island. "It's a very successful program,” Hall said. “The basic model continues to be productive. The last live snake to have escaped Guam was back in 2006 in a munitions container that ended up in Oklahoma." Mitigation efforts have also been unfolding with success. In 2011, 135 acres of jungle on Andersen Air Force Base were designated as a Habitat Management Unit (HMU) for ecological study.
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Leanne Obra, JRM Brown Tree Snake program manager, explained that the HMU started as a multi-species barrier enclosure, or fenced area designed to keep out invasive snakes, pigs, and deer. The barrier helps control the area for environmental study on the snake population. The fencing surrounding the site has been rendered snake-proof via a large protruding bump on the fence line four feet above the ground.
"The snakes can't climb over it because the bump requires them to put about two-thirds of their body weight upside down, and their tails can't support that," Obra said.
The HMU has been a haven for scientific study on forest recovery and a measuring stick for the ecological health of the island. Because the snake population within the HMU can be closely observed for signs of environmental impact, the area is perfect for conducting routine bait drops in the battle against the invasive snake.
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The bait drop is an essential part of Brown Tree Snake mitigation. A multi-day helicopter drop occurs every 90 days and is coordinated with the USDA. The mitigation is conducted using a UH-6 helicopter custom fitted with an automated bait dispenser.
The helicopter makes several passes over the HMU while the automated dispenser drops Tylenol-laced bait into the trees. The bait presents itself as an easy snack for the arboreal brown tree snake, but the snakes have proteins in their blood that cannot function after ingesting Tylenol. Over the past five years, the Brown Tree Snake Program has dropped 46,200 baits in the HMU, and the effect is noticeable. The environmental experts managing the area notice that it’s harder and harder to find the snake species within the HMU, and signs point to a dwindling population. "We continue to coordinate with our partners, operations personnel, and administrators to not only prevent the spread of Brown Tree Snake from Guam but to suppress and control Brown Tree Snake numbers to reduce their impact on the island of Guam and to restore the island's ecosystems," Obra said. (Joint Region Marianas)
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