New Technology Targets Invasive Brown Treesnakes from the Air

by United States Department of Agriculture: Animal and Plant Health Inspection Service
Stripes Guam

This summer, USDA’s Animal and Plant Health Inspection Service (APHIS) Wildlife Services program (WS), in partnership with a group of government agencies and a private engineering firm, made great strides in the delivery of a new tool to combat invasive brown treesnakes on Guam. 

The technology uses acetaminophen-treated dead mouse baits attached to biodegradable streamer-like cartridges. Launched from a helicopter or airplane, the baits are designed to snag in trees where the snakes feed. While prior tests have been conducted on Guam since 2004 to investigate, and ultimately prove, the feasibility of this technique, those tests used small numbers of hand-made baits manually dropped from a helicopter. This summer’s test employed machine-made baits automatically deployed in large numbers at high speed.

This project was done in collaboration with the Government of Guam, Department of Defense (DoD), the Department of the Interior’s (DoI) Office of Insular Affairs and U.S. Fish and Wildlife Service, and a private engineering firm.

“This effort is a culmination of over 20 years of research. Since 1994, Wildlife Services scientists and operations personnel have systematically developed and evaluated tools to control brown treesnakes. These tools include snake traps, baiting stations, snake-sniffing detector dogs at ports and airports, chemical repellents, and fumigants,” states Robert Gosnell, WS State Director on Guam.  “The successful aerial delivery of baits is a critical next step towards the control of brown treesnakes over large areas, including remote and inaccessible areas of Guam.”

In July, WS scientists from the National Wildlife Research Center (NWRC) and their partners tested this new system, deploying baits from a helicopter on a 110-hectare (270-acre) demonstration site within DoD’s Andersen Air Force Base. (Watch online video of aerial bait drops). Snake activity at the research site will be monitored over the next year to determine the impacts of the baiting and guide future efforts to control or eradicate the brown treesnakes in strategic locations for the recovery of native wildlife species.  Reducing snake numbers also helps prevent the accidental transport of snakes to other islands.  Ultimately, this technology may be used to suppress snake populations island-wide.  Preliminary results from the initial bait drops are already showing a reduction in snake activity.

“We worked with engineers from Applied Design Corporation—a technology development company based in Boulder, Colorado— to design a machine-made bait cartridge and a GPS-enabled automated delivery system that can rapidly and accurately deliver baits from an aircraft over large forested areas,” notes Dr. Shane Siers, lead NWRC researcher for the project.  “The current system delivers baits at a rate of up to four per second, ensuring we get the appropriate bait coverage in Guam’s dense forest canopies. It was also essential that the final product was cost-effective. If it proves to be successful here on Guam, the device could be adapted for other invasive species management efforts.”

Extensive scientific research, field observations, and video monitoring—in addition to the findings of an environmental risk assessment required for this effort—confirm that this method is humane to snakes and presents little risk to non-target species. Brown treesnakes ingesting the small dose of acetaminophen (80 milligrams) will die within about 24 hours with no signs of distress. Given the baits are hung in trees, distributed at low densities, and eaten quickly by the snakes, there will be very limited exposure of the baits to non-target species.  Moreover, this project poses no risk to humans, and aquatic life will not be affected because there is no surface water present in the targeted areas.

The brown treesnake is an invasive species unintentionally introduced to Guam in the late 1940s.  With no native predators, the snake’s population in Guam has grown to an estimated 1 to 2 million.  The brown treesnake is responsible for the disappearance of most native bird, bat, and lizard species on the island.  The snake has also caused extensive damage to the island’s economy and electrical grid, costing an estimated $1-4 million annually in lost productivity due to power outages.

The unintentional movement of brown treesnakes as a result of shipping or travel represents a very real danger to all islands in the western Pacific basin and sections of the U.S. mainland.  The economic costs of potential brown treesnake  introduction to the Hawaiian Islands alone are estimated to be as high as $2 billion annually—in addition to the severe ecological damage the snake would cause to native birds and other wildlife.  Since 1993, more than 150,000 brown treesnakes have been removed from areas of high transport risk in Guam (airports, seaports, etc.), and the majority of outbound cargo is thoroughly inspected for snakes. A result of these successful Federal, State, and local cooperative efforts is that no live brown treesnakes have been detected at Hawaiian ports-of-entry in almost 20 years.

“Though our containment efforts have been highly successful and we’ve kept the snakes from getting off of Guam, we’re now expanding our focus to remove snakes from the more remote areas on the island. With these new tools and strategies, brown treesnake management may soon be making even bigger strides toward its ultimate goal of reintroducing native birds to the island,” notes Gosnell. “It’s an exciting time to be working on this project.”

For more information on WS’ efforts to manage brown treesnakes and protect endangered species on Guam, please visit
• Battling the Brown Treesnake: Aerial Bait Drops on Guam (video)
• WS–National Wildlife Research Center – Brown Treesnake Research
• WS–Brown Treesnake Damage Management
• WS–Guam FY15 State Report
• APHIS YouTube–Brown Treesnake (b-roll)
• APHIS Flickr–Brown Treesnake (photos)

The WS is a program with the USDA Animal and Plant Health Inspection Service.  Its mission is to provide Federal leadership and expertise to resolve wildlife conflicts to allow people and wildlife to coexist. The program’s efforts help people resolve wildlife damage to a wide variety of resources and to reduce threats to human health and safety. Funding for the WS Program is a combination of federal appropriations and cooperator-provided funds.

The National Wildlife Research Center is the research arm of the WS program.  It is the only Federal research organization devoted exclusively to resolving conflicts between people and wildlife through the development of effective, selective, and socially responsible methods, tools, and techniques.

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