USGS Brown Treesnake Research Continues at Guam National Wildlife Refuge

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On May 14, Director Reilly signed a Memorandum of Agreement with the Department of the Navy and the U.S. Fish and Wildlife Service. The MOA provides for continuity of operations for the USFWS and the USGS with construction of new office and lab facilities on the Guam National Wildlife Refuge in conjunction with DOD’s construction of a Marine Corps firing range.

“The USGS has a long history of collaborating with the Department of Defense in support of U.S. facilities and force readiness in the INDOPACOM Area of Responsibility.  One of our signature efforts ongoing today is a collaboration with DOD, the U.S. Fish and Wildlife Service, and the local government in minimizing the impacts of the invasive Brown Treesnakes (BTS) and improving BTS controls on military lands on Guam,” said Jim Reilly, director of the USGS.

Agency Leaders Sign Guam Memorandum of Agreement Virtually

Karnig Ohannessian, Deputy Assistant Secretary of the Navy (Environment), Jim Reilly, Director, USGS, and Aurelia Skipwith, Director U.S. Fish and Wildlife Service virtually signing a Memorandum of Agreement. for continuity of operations on the Guam National Wildlife Refuge.

(Public domain.)


USGS scientists and staff associated with the Brown Treesnake Project are co-located at the Guam National Wildlife Refuge at the northern end of Guam in the western Pacific Ocean. Project staff are developing and testing control tools for invasive Brown Treesnakes, as well as understanding their impacts on Guam's ecosystems. Project staff also lead the multi-agency Brown Treesnake Rapid Response Team, which responds to invasive snake sightings throughout the Pacific and trains personnel from cooperating agencies to increase the capacity of the team. Major partners of the USGS Brown Treesnake Project include DOI Office of Insular Affairs, USDA-APHIS Wildlife Services, Department of Defense, the U.S. Fish and Wildlife Service, and State and Island governments.

Biologists prepare for a Visual Survey of Brown Treesnakes

The USGS biologist crew prepares for a visual survey for Brown Treesnakes (BTS) within the Habitat Management Unit (HMU) on Guam. The HMU is a 55-hectare fenced area designated for conservation of native species, and resource-management agencies share the goal of suppressing or eradicating BTS within the HMU. The HMU has received multiple applications of an aerially distributed snake toxicant to assess the feasibility of snake control in forests at a large scale. Searchers using visual surveys detect snakes of all sizes making surveys a valuable tool to monitor the effects of snake control.

(Credit: Amy Yackel Adams, USGS. Public domain.)

2016 Brown Treesnake Visual Survey, Saipan

A former Rapid Response Team (RRT) Coordinator (Adam Knox) supervises and organizes the deployment of the Rapid Response Team following credible sightings of Brown Treesnakes (BTS) on the island of Saipan in 2016. The RRT Coordinator, stationed on Guam, is responsible for organizing the network of trained members and specialists that comprise the RRT, receiving reports, conducting interviews, and assessing the credibility of sightings with the assistance of researchers based in Fort Collins, CO. The position is primarily supported by long-term funding commitments from the US DOI Office of Insular Affairs (OIA). OIA is a leading partner in supporting detection and control tool development aimed at refining BTS management and protecting Pacific Islands from BTS. 

(Credit: Patrick Barnhart, USGS. Public domain.)

Scientist Measures Hand-Captured Brown Treesnake

University of Guam biologist, Peter Xiong, measures a Brown Treesnake that he captured by hand during a visual survey for Brown Treesnakes (BTS) in the Habitat Management Unit on Guam. The University of Guam represents an important local partner for supporting research efforts on control and containment of BTS in the Pacific Region. They hire and maintain snake biologists that collaborate with USGS scientists on multiple projects supported by DOI Office of Insular Affairs, Department of Defense, and USGS.

(Credit: Amy Yackel Adams, USGS. Public domain.)

Accidentally introduced to Guam during or soon after World War II, the Brown Treesnake was a major contributor to the loss of nine of 11 native forest birds and several native lizard and bat species on the island. Some of these lost species are present in captivity or on other islands in the Marianas, suggesting that recovery of some of Guam’s native biota may be possible. However, prospects for successful recovery are dependent on successfully controlling or eradicating Brown Treesnakes at various spatial scales.

Much of the research conducted by USGS scientists is directed towards improving methods for Control and Landscape-Scale Suppression of the Invasive Brown Treesnake by developing, testing, and validating control tools and by improving understanding of the species’ biology, ecology, and behavior for control purposes. The USGS Brown Treesnake Project is led by Fort Collins-based principal investigators who oversee research activities conducted by USGS scientists, affiliates from the University of Guam, and cooperators; these projects are aimed at containment, control, management, and detection of the invasive Brown Treesnakes on Guam.

2016 Brown Treesnake Rapid Response Team

The Rapid Response Team contains members from multiple groups and agencies. There is a core group of biologists stationed on Guam that are highly adept at finding and capturing BTS. These biologists will deploy within 24-48 hours of a snake sighting to the island the snake was seen on. The RRT also contains members from cooperative groups and agencies on the Federal, State, and Local level stationed on islands throughout the Pacific region. Having trained members on snake free islands that may receive BTS is key to mounting a fast and effective response to snake sightings. These members help verify snake sightings, interview the person(s) that saw the snake, and begin the initial response before the Guam group arrives.

(Credit: Patrick Barnhart, USGS. Public domain.)

2014 Brown Treesnake Rapid Response Team

The Brown Treesnake (BTS) Rapid Response Team includes members from a wide range of entities and agencies. A core group of Guam-based biologists who are experts at finding and capturing  snakes (skills that are continuously honed through their field research activity on Guam) provide assistance to local cooperators during a response. These biologists deploy within 24-48 hours of a reported credible BTS sighting. Team membership includes representatives from non-profit entities and Federal, State, and Local Government agencies operating in the Pacific Region. Presence of trained local members on snake free islands is key to mounting a fast and effective response when BTS sightings are reported. These members help verify sightings of BTS, interview the person(s) that saw the snake, and begin the initial response before USGS partners arrive to provide assistance.

(Credit: Patrick Barnhart, USGS. Public domain.)

2019 Brown Treesnake Rapid Response Team Training

Brown Treesnakes are incredibly difficult to find in the dense vegetation common on islands throughout the Pacific Region, and many people have a natural fear of snakes. A primary function of the Brown Treesnake Rapid Response Team is to provide in-depth training to ensure team members are affective in finding and capturing snakes in the field. Trainees also learn how to set up, maintain, and check snake traps, create transects and conduct visual surveys, capture and handling of a range of snake species, and techniques for interviewing someone reporting a snake sighting. All team members attend an initial 2-week course and follow up with a refresher course every two years to re-sharpen their skills and maintain membership on the Team.

(Credit: Patrick Barnhart, USGS. Public domain.)


The devastating ecological impacts of Brown Treesnakes on Guam would likely be replicated if the snakes were to become established elsewhere in the Pacific, including Hawai’i or the U.S. Commonwealth of the Northern Mariana Islands. Because Brown Treesnakes are stealthy and often hide in cargo or goods, the risk of accidental transportation of snakes from Guam is high. Partners at USDA-APHIS Wildlife Services conduct highly effective snake trapping and cargo inspections around ports and airports on Guam, and state/territorial partners repeat these actions on recipient islands. However, some Brown Treesnakes have made it through these interdiction nets in the past.

Brown Treesnake Eating a White Tern

A Brown Treesnake (BTS) eating a white tern on northern Guam. This observation was made during ongoing field work to refine snake control strategies in military housing. Snakes are capable of consuming very large prey items, and the snake successfully swallowed the tern. The Department of Defense maintains ongoing BTS interdiction efforts to control the abundance of BTS on military property and minimize the likelihood the snake is accidentally transported off the island of Guam. Due to these interdiction efforts, snake densities are reduced around military housing, which provides some refuge in these areas for a remaining species of native bird (the Micronesian starling). USGS partners with Department of Defense to develop and optimize control strategies in forested and urban locations.

(Credit: Nathan Sablan, USGS. Public domain.)

Brown Treesnake Consumes Gecko

Juvenile Brown Treesnakes (BTS) prefer to eat cold-blooded species like geckos and skinks. This snake was encountered consuming a locally abundant gecko, also thought to be a human introduction to Guam. The abundance of nonnative prey on Guam supports BTS populations and poses challenges to suppression of snakes for native species recovery. 

(Credit: Melia Nefus, USGS. Public domain.)

Guam Rail Running Across Trail

An endemic ko'ko' (Guam rail) running across a trail on Cocos, an offshore island located at the southernmost tip of Guam. Cocos is the only location on Guam that has allowed native species to persist in the absence of non-native species such as rats, cats, and snakes. Rails were introduced to the island after an island-wide rat eradication effort. Since then, they have successfully established and spread across the island, demonstrating that native species can recover when invasive predators are controlled. 

(Credit: Peter Xiong, USGS. Public domain.)


The USGS-led Brown Treesnake Rapid Response Team (RRT) stands ready when a credible snake sighting is reported on a snake-free island. The RRT conducts intensive training sessions on Guam for non-USGS team members stationed elsewhere: courses include extensive visual searching to improve searchers’ ability to see snakes based on USGS research outcomes on optimal search patterns, as well as training on use of snake traps and collection of high-quality data. In the event of a credible sighting, Guam-based staff with the USGS Brown Treesnake Project travel to the site to provide expert assistance to local partners during a response, which is focused on determining whether an incipient population of snakes is present. RRT response strategies incorporate USGS research results, such as improving snake detectability at low densities, increasing effectiveness of control tools in rodent-rich environments, and predicting movements of snakes translocated accidentally to maximize the likelihood of capture success.