U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2014–3076

March 2015

FORT COLLINS SCIENCE CENTER

Invasive Species Science Branch

Research and Management Tools for Controlling Invasive Species

Biology, Impacts, and Control of Invasive Reptiles

Invasive species are considered to be second only to 

habitat degradation in terms of negative impacts on the Earth’s 

ecosystems, and our scientists make up a significant proportion of the global expertise in the rapidly-growing problem 

of invasive reptiles. Long-term research on Guam has led to 

development and validation of numerous effective control 

tools, while more recent research in Florida and elsewhere 

focuses on understanding impacts and control opportunities for 

Photograph from USGS.

Capabilities

Invasive, nonnative species of plants, animals, and disease organisms adversely affect the ecosystems they enter. Like “biological 

wildfires,” they can quickly spread and affect nearly all terrestrial and 

aquatic ecosystems. Invasive species have become one of the greatest 

environmental challenges of the 21st century in economic, environmental, and human health costs, with an estimated effect in the United States 

of more than $120 billion per year. Managers of the Department of the 

Interior (DOI) and other public and private lands often rank invasive species as their top resource management problem. The Invasive Species 

Science (ISS) Branch of the Fort Collins Science Center (FORT) provides 

research and technical assistance relating to management concerns for 

invasive species, including understanding how these species are introduced, identifying areas vulnerable to invasion, forecasting invasions, 

and developing control methods. To disseminate this information, branch 

scientists are developing platforms to share invasive species information with DOI cooperators, other agency partners, and 

the public. From these and other data, branch scientists are constructing models to understand and predict invasive species 

distributions for more effective management. The branch also has extensive herpetological and population biology expertise 

that is applied to harmful reptile invaders such as the Brown Treesnake on Guam and Burmese Python in Florida.

Photograph from Björn Lardner, Colorado State University.

Burmese pythons and other recent invaders. Branch scientists 

combine extensive herpetological expertise with cutting-edge 

quantitative skills to estimate detection probability, population 

size, and eradication prospects for a range of invasive reptiles. 

Projects and collaborators span the globe, from the western 

Pacific Ocean, across the United States mainland, to Puerto 

Rico and beyond.

Species Distribution Modeling

A requirement for managing a species, be it a common 

native species, a species of conservation concern, or an invasive species, is having some information on its distribution 

and potential drivers of distribution. Branch scientists have 

been tackling the question of where these types of species are 

and where they might be in the future. Focus species are as 

varied as the invasive tamarisk, Russian olive, Africanized 

honey bee and nutria to the federally threatened Lesser Prairie 

chicken and others. These and other species are modeled at a 

variety of spatial scales, from park or wildlife refuge to global 

levels. Models use various predictor layers that can include 

current and future climate layers (near- and long-term projections), remote-sensing derivatives (such as MODIS phenology 

metrics), land cover, topography, and anthropogenic features.
Selected Projects

Resource for Advanced Modeling

Branch scientists have developed the Resource for Advanced 

Modeling (RAM), a modeling facility for collaborative research both 

within the U.S. Geological Survey (USGS) and with the wider research 

community. The RAM brings together remote sensing and climate 

forecasting experts, habitat modelers, field ecologists, and land managers 

in a synergistic environment conducive to species distribution modeling. 

The branch has also helped develop a modeling program called Software 

for Assisted Habitat Modeling (SAHM) in the VisTrails1 platform which 

researchers use to create habitat models for species of interest to resource 

managers. The program provides a significant capability to run, in a 

consistent and repeatable manner, five different habitat models (Maxent, 

Boosted Regression Trees, Logistic Regression, Multivariate Adaptive 

Regression Splines, and Random Forest). SAHM combines predictor 

layers with user-collected field sampling measurements for a particular 

species. The program uses these data to run statistical models that analyze habitat requirements of a species of interest and predict the potential distribution based on habitat suitability. Model outputs can help 

users, such as resource managers, generate predictive maps or reports to aid in predicting and managing the spread of invasive species.

Photograph from USGS.

1

Any use of trade, industry, or firm names in this report is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Control and Landscape-Scale Suppression of the Invasive 

Brown Treesnake

The Brown Treesnake is a highly destructive reptile species that has extirpated many native species of birds, bats, and 

lizards from the U.S. Territory of Guam. For more than two 

decades branch scientists with the Invasive Reptile Project 

have developed, validated, and tested the feasibility of Brown 

Treesnake control and suppression at various spatial scales. An 

important aspect of our research is increasing the efficacy of 

control tools (rodent-baited traps, toxicants delivered aerially 

and by bait tubes, and visual searches). Our recent island-wide 

visual surveys along road edges have revealed a high proportion of juvenile snakes across Guam; this is an important 

finding because juveniles consistently evade our control tools. 

To further understand juvenile distribution, we are attempting 

to learn habitat associations for these juveniles by conducting 

visual surveys on forest edges and interiors. Increased understanding of juveniles is crucial because a large proportion of 

Brown Treesnakes escaping Guam on cargo, ships, and airplanes are juveniles. Landscape-scale suppression techniques 

have improved because of new control technologies developed by U.S. Department of Agriculture (USDA) and partner 

agencies, chiefly aerial delivery of toxicant-loaded bait. Our 

scientists are contributing to the development of these methods 

through control tool validation (for example, confirming that 

the tool is functioning to eradicate all vulnerable individuals) 

and by modeling the optimal timing of successive toxicant 

drop applications. Our cooperators include U.S. Department 

of the Interior Office of Insular Affairs, U.S. Fish and Wildlife 

Service (USFWS), U.S. Navy, U.S. Air Force, Guam Division 

of Aquatic and Wildlife Resources, USDA Wildlife Services, 

Hawaii Department of Agriculture, Hawaii Department of Forestry and Wildlife, and Commonwealth of the Northern Mariana 

Islands Department of Fish and Wildlife.

Decision Support for Invasive Species—A Buffelgrass 

Example

African buffelgrass (Pennisetum ciliare) is spreading rapidly across the desert southwest of the United States, 

creating novel fire risks in both natural and urban areas and 

threatening conservation efforts. Left unchecked, buffelgrass can dominate the desert landscape and cause regular, 

fast-moving wildfires that threaten natural resources within 

public lands and adjacent urban neighborhoods, ruin viewscapes, close popular attractions, and even interrupt essential 

services. Southwestern deserts are peppered with national 

parks, national forests, Bureau of Land Management lands and 

urban areas. The growing fire risk and environmental damage through the entire region could impact tourism, decrease 

property values, and make it harder to attract good employers and retain high-skilled workers. Buffelgrass invasion also 

jeopardizes ecosystem health, ecological goods and services, 

and conservation measures, including protection of threatened 

and endangered species. Branch scientists have been working 

with the National Park Service and other public land managers 

in these areas to develop a decision support model to enhance 

planning and target their limited funds most effectively. These 

models present a prioritized and disciplined strategy while 

providing flexibility through adaptive management. The state 

and transition model simulates buffelgrass spread and treatment effectiveness using incomplete distributional data and 

distribution maps as inputs. With these models, land managers 

have the potential to make informed and effective decisions to 

maximize their limited resources.

Photograph from Leonardo Frid, ApexRMS.
Ecology and Control of Invasive Reptiles in Florida

The Florida Everglades encompass a vast subtropical ecosystem 

including Everglades National Park, which is the only place in the 

United States designated as a World Heritage Site, an International 

Biosphere Reserve, and a Wetland of International Significance. Billions of dollars have been committed to the long-term restoration of 

this ecosystem, but burgeoning populations of introduced and invasive reptiles threaten prospects for restoration. The Burmese python is 

the most widely known of these invaders, and this giant snake appears 

to have contributed to drastic declines among several species of midsized mammals in the Everglades. However, other large predatory 

species including the Argentine tegu and Northern African Python 

are also established in southern Florida, and the potential impacts of 

these species are not widely understood. FORT scientists are conducting research on a range of detection and control tools for invasive 

reptiles in Florida, including environmental DNA sampling methods, 

trap development and field testing, and validation of visual searching 

efficacy. Scientists are also conducting basic ecological research to better understand impacts of these invasive predators and to 

identify ecological or behavioral vulnerabilities that can be exploited by control tools.

Modeling Invasive Species Distribution—A Nutria Example

Nutria or coypu (Myocastor coypus) are invasive rodents 

native to South America that cause wetland degradation and have 

become established in many parts of the world, including the Southeast and the Pacific Northwest within the United States. Large-scale 

management of the species requires knowledge of its potential distribution. Working with researchers at the USGS National Wetlands 

Research Center, we are developing models of potential distribution 

in the United States. Branch scientists have created a physiological 

model built on cold temperature limitations and a statistical model 

based on creating relationships between observations and environmental characteristics at the locations. Using these base models, our 

objective is to develop a comprehensive model of potential suitable 

habitat for nutria globally and within the United States. This model 

can be applied to future climate scenarios to determine how nutria 

distribution may change, guiding management efforts including 

highlighting areas for early detection.

Photograph from Paul Andreadis, Denison University.

Photograph from USGS.

Brown Treesnake Rapid Response Team

Brown Treesnakes continue to cause major problems for the ecology, economy, and quality of life on Guam. In 2002, a multiagency Rapid Response Team (RRT) led by USGS was established to assist with detection and capture of Brown Treesnakes on 

recipient islands if a snake was accidentally transported from Guam. The RRT has incorporated a wide range of research results 

from the USGS Invasive Reptiles Project, such as means to improve snake detectability at low densities, effectiveness of control 

tools in rodent-rich environments, and predicting movements of snakes translocated accidentally. The primary RRT activities are 

conducting training courses on Guam for team members stationed on other islands and conducting and managing multi-agency 

responses when a snake is sighted on an island other than Guam. Training courses on Guam include extensive visual searching 

to develop the ability to find and capture snakes, as well as instruction on use of snake traps and proper interview techniques 

when gathering snake observation data from the public. The Rapid Response Team coordinator also performs outreach and public 

education on Brown Treesnakes throughout the Pacific region. Cooperators include the DOI Office of Insular Affairs, USFWS, 

U.S. Commonwealth of the Northern Mariana Islands, U.S. Department of Defense, USDA Wildlife Services, Guam Division of 

Aquatic and Wildlife Resources, Hawaii’s Coordinating Group on Alien Pest Species and Invasive Species Committees, Hawaii 

Department of Agriculture, and Hawaii Department of Forestry and Wildlife. Additional quarantine, agriculture, and natural 

resources cooperators include officials from the Federated States of Micronesia, the Republic of the Marshall Islands, and the 

Republic of Palau.
Contact Information

Bob Reed, Ph.D., Branch Chief

U.S. Geological Survey 

Fort Collins Science Center

2150 Centre Avenue, Building C

Fort Collins, Colorado 80526-8118

Tel. 970.226.9464 Fax 970.226.9230

reedr@usgs.gov

Learn more about FORT science, products, and 

resources at http://www.fort.usgs.gov

Invasive Species Science Branch Web site: 

http://fort.usgs.gov/ISS/

Photograph from Leá Bonewell, USGS.

Research to Support Bird Restoration and Recovery on Guam

On Guam, the endangered Mariana swiftlet is a bird species 

restricted to three caves on Naval Base Guam while many other 

native birds are either extinct or awaiting reintroduction (for 

example, Guam Rail). The invasive Brown Treesnake (BTS) 

played a major role in the loss of native avifauna and may be preventing swiftlet population recovery and limiting the potential for 

reintroductions. Operational BTS trapping by the USDA Animal 

and Plant Health Inspection Service (APHIS) Wildlife Services 

reduces BTS in areas of concern across Guam. For example, 

trapping occurs in the vicinity of swiftlet-occupied caves, but 

surveys suggest that BTS frequently penetrate the trap ring and 

access caves. If the few BTS that penetrate the trap ring become 

resident after entering the cave, a small number of BTS could 

have a disproportionate impact on swiftlet populations. Similarly, 

the Guam National Wildlife refuge has recently installed a fence 

to exclude BTS and initiated a trapping program to reduce snake 

populations and create conservation space for potential avian 

reintroductions. Branch scientists are working with these Federal 

agencies to assess the efficacy of control tool deployment in 

areas of conservation concern. Research focuses on (1) the best 

control tool deployment methods for optimizing BTS interception rates and decreasing predation on prey of conservation concern; and (2) understanding levels of BTS suppression required 

to reduce snake predation on birds to levels that allow persistence 

of native bird populations.

Photograph from Björn Lardner, Colorado State University.

Staff

Branch Chief: Bob Reed, Ph.D., Supervisory Research

 Wildlife Biologist, reedr@usgs.gov

Colorado-based staff:

Bonewell, Lea, B.S., Project Manager, bonewelll@usgs.gov

Jarnevich, Catherine, Ph.D., Ecologist, jarnevichc@usgs.gov

Klug, Page, Ph.D., Ecologist, pklug@usgs.gov

Yackel Adams, Amy, Ph.D., Statistician, yackela@usgs.gov

Hayes, Mark, Ph.D., Contracted Ecologist, hayesm@usgs.gov

Florida-based staff:

Falk, Bryan, Ph.D., Biologist, bfalk@usgs.gov

McEachern, Michelle, B.S., Biological Science Technician, 

 mmceachern@usgs.gov

Guam-based staff:

Knox, Adam, M.S., Rapid Response Coordinator, 

 aknox@usgs.gov

Tadevosyan, Tigran, Ph.D., Contracted Research Manager,

 ttadevosyan@usgs.gov

Contracted Biologists: Barnhart, Patrick, B.S., Hinkle, Thomas, 

B.S., Hogan, Michael, B.S., Holldorf, Elden, B.S., Kaseman, 

Justine, B.S., Robinson, Charlotte, B.S.

St. Aublin, Gregory, Contracted Biologist

Marijoy Viernes, Contracted Biologist

Colorado State University cooperators:

Savidge, Julie, Ph.D., Ecologist, Julie.Savidge@colostate.edu

Lardner, Björn, Ph.D., Ecologist, lardnerb@usgs.gov

Siers, Shane, Ph.D., Ecologist, siers@usgs.gov

ISSN 2327-6932 (online)

http://dx.doi.org/10.3133/fs20143076