Contact Information: 

Dr. William Pitt 

Supervisory Research Wildlife Biologist 

Hawaii Field Station

P.O. Box 10880

Hilo, HI 96721

Phone: (808) 961-4482

FAX (808) 961-4776

will.pitt@aphis.usda.gov

www.aphis.usda.gov/wildlife_damage/

nwrc/ 

Major Cooperators

 Guam

 Hawaii Agriculture Research Center

 Hawaii Department of Land and Natural Resources

 Hawaii Department of Agriculture

 Hawaiian Commercial and Sugar

 Hawaii Macadamia Nut Growers Association

 Hilo International Airport

 Kamehameha Schools (Bishop Estate)

 MacFarms of Hawaii

 Mauna Loa Mac Nut

 Monsanto Corporation

 Nature Conservancy

 Pioneer Hi-Bred Seed

 Syngenta Corporation

 Tropical Fruit Growers of Hawaii

 University of Hawaii 

 U.S. Fish and Wildlife Service

 U.S. Department of Defense

Wildlife Services

Protecting People rotecting People

Protecting Agriculture rotecting Agriculture

Protecting Wildlife rotecting Wildlife

FY 2012

National Wildlife Research Center

United States Department of Agriculture

Animal and Plant Health Inspection Service

National Wildlife Research Center Scientists Develop Methods to Reduce 

Damage Caused by Invasive Species 

Wildlife Services’ (WS) National Wildlife Research Center (NWRC) is the only Federal 

research facility devoted exclusively to resolving confl icts between people and wildlife 

through the development of effective, selective, and socially responsible methods, tools, 

and techniques. NWRC’s fi eld station in Hilo, Hawaii, is ideally located to allow research 

biologists to develop methods needed to control invasive species damage to agricultural 

crops and native ecosystems on islands.

Oceanic islands like the Hawaiian archipelago are more susceptible to the impacts of 

invasive species than mainland areas because remote islands evolved in ecological isolation and have few predators or competitors, have a lot of air and sea traffi c, and typically 

provide a favorable habitat and climate for many introduced species. Further, native species on the islands have evolved in the absence of many introduced threats and usually 

respond poorly to invasive animals or disease.

Invasive species are one of the greatest threats to Hawaii’s agricultural economy, natural 

environment, and the health and lifestyle of Hawaii’s people. Invasive vertebrate species cause millions of dollars worth of crop losses, the extinction of native species, the 

destruction of native forests, the spread of disease, and threats to the health and safety 

of residents. Scientists at the NWRC Hilo, Hawaii, fi eld station are investigating a variety 

of methods to reduce damage caused by invasive species such as rodents, Coqui frogs, 

brown treesnakes, invasive birds, mongooses, and feral ungulates in Hawaii as well as 

throughout Pacifi c islands linked to Hawaii through transport and trade. 

Applying Science and Expertise to Wildlife Challenges

Ensuring Safe Rodent Eradication Efforts—Rodenticides are used to eradicate invasive 

rodents from islands throughout the world. In 2011, the Palmyra Atoll Rainforest Restoration Project (composed of the U.S. Fish and Wildlife Service, The Nature Conservancy of 

Hawaii, and Island Conservation) attempted to eradicate rats from Palmyra Atoll (a remote 

island in the Pacifi c Ocean, approximately 1,000 miles south of Hawaii) in an effort to 

enhance the biodiversity of seabirds, native plants and terrestrial invertebrates. The eradication was implemented by applying Brodifacoum 25W Conservation, a rodenticide bait 

containing the second generation anticoagulant rodenticide brodifacoum, by air and ground 

application. Because the eradication effort used an APHIS pesticide label and implementation of the control operation required a label variance, the coalition contracted with NWRC 

to monitor the eradication’s environmental effects. NWRC scientists measured the application rate and bait distribution on the ground following aerial application and documented 

the fate of bait, collected potential nontarget mortalities, and systematically collected soil, 

water, insects, geckos, fi sh, and crabs to determine environmental residue levels. NWRC’s 

goal was to help evaluate any secondary hazards associated with the eradication effort. 

Researchers found the overall rodenticide application rate to be within the limits specifi ed 

by the Environmental Protection Agency’s approved supplemental label. However, they 

also documented bait in the aquatic environment and considerable variation in the amount 

applied over small localized areas. Bait may have ended up in the aquatic environment 

due to shoreline confi guration, island topography, overhanging vegetation, bird activity affecting baiting aircraft fl ight lines, wind strength and direction, pilot experience, and 

weather conditions at the time of the bait drop. 

NWRC researchers found rodenticide residues in ants, cockroaches, geckoes, hermit 

crabs, fi ddler crabs, and black-spot sergeant fi sh that were collected alive as part of 

scheduled environmental sampling activities during and after bait application. Fifty-one 

animal samples representing 15 species of birds, fi sh, reptiles, and invertebrates were 

Managing Invasive Species Impacts to anaging Invasive Species Impacts to 

Agriculture, Natural Resources, and Human griculture, Natural Resources, and Human 

Health and Safety ealth and Safety

Groups Affected By These Problems

 Commercial transportation industry

 Farmers/Homeowners

 Horticulture industry

 Natural resource managers

 Seed crop industry

 Tropical fruit and nut producers

 Wildlife and refuge managers
found dead and collected for residue analysis during systematic 

searches or collected opportunistically as potential nontarget 

mortalities during regular activities throughout the atoll. NWRC 

researchers detected rodenticide residues in 12 of 15 birds that 

were found dead on or around the atoll after the broadcast application. Affected avian species included bristle-thighed curlews, 

Pacifi c golden plovers, ruddy turnstones, and wandering tattlers. 

Affected non-avian species included mullet fi sh and Cardisoma 

spp. land crabs. Nontarget exposure to the rodenticide likely was 

a result of direct consumption of bait and secondary exposure 

through scavenging of poisoned rat carcasses. 

More than one live rat was detected in July 2011, necessitating 

a third broadcast application of rodenticide bait over part of the 

Atoll. Rats have not been detected after the fi nal broadcast. 

Monitoring for the presence of rats will continue through the 

summer of 2013 to determine whether rat eradication has been 

achieved. This type of collaboration, evaluation, and monitoring 

is critical to the success of the current project as well as future 

eradication projects.

Bait Delivery for Brown Treesnakes—The invasive brown 

treesnake has caused extensive economic and ecological damage to the Island of Guam. WS operational and research experts 

work on a variety of fronts to reduce damage caused by these 

snakes. In cooperation with Applied Design Corporation, a private 

engineering fi rm, NWRC scientists designed an automated 

aerial bait delivery system for use in brown treesnake control 

efforts. The fi rst phase of the system’s development is complete 

and consists of the bait delivery device. Additional components 

that remain to be developed include the design of bait package 

manufacturing equipment, integrated helicopter electronics, and 

integrated software systems. Once completed, this aerial delivery system will allow for the economical delivery of toxic brown 

treesnake bait to large, remote, and rugged areas of Guam.

Sources of Island Rats—Rodent control on islands to protect 

nesting seabirds and other threatened wildlife is an important 

conservation activity. When rats reappear after an eradication 

effort, it is important to know whether eradication was incomplete 

or whether the island was recolonized. Using genetic analyses, 

NWRC researchers showed that in the case of Lehua Island, 

Hawaii, the reemergence of rats was due to an incomplete eradication effort and not new colonizations. This fi nding has led to 

reevaluations of rat eradication strategies and efforts.

Diphacinone Residue in Feral Swine—NWRC researchers 

examined feral swine tissues to determine whether the potential 

hazard of consuming meat from swine previously exposed to 

diphacinone rodenticide baits was reduced by cooking. Cooking 

had little effect on residual diphacinone concentrations, the highest concentration of which was found in the liver tissue. Accordingly, NWRC researchers caution that the consumption of swine 

meat obtained from areas with active rodent control programs 

should be avoided.

Biosecurity Assessment for U.S. Military Operations in 

the Pacifi c—In 2006, the U.S. Department of Defense (DoD) 

proposed to restructure military assets in the Pacifi c, including 

relocating 8,600 Marines plus their dependents from Okinawa, 

Japan, to Guam. In addition to this translocation, the military also 

proposed to construct both inland and port facilities to support 

the move and future training, as well as additional offi ces, homes, 

and other facilities on Guam. Both the short term and long term 

increase of military activity over the next 10 years will result in an 

increase in the movement of cargo and people into Micronesia 

from Asia, the United States, and other parts of the world. With 

this increase in movement, the potential for the introduction of 

invasive species and wildlife-borne diseases also increases. 

In an unprecedented effort, WS, along with other APHIS 

programs, the U.S. Geological Survey, and the Smithsonian Institute, assisted the DoD in the development of a risk 

assessment and biosecurity plan for Guam and the rest of Micronesia. WS’ part of the assessment identifi ed and quantifi ed 

potential routes of introduction and the risks of introduction of 

1) wildlife-related pathogens, such as rabies, avian malaria, 

West Nile virus, and H5N1 avian infl uenza virus, and 2) invasive species, such as brown treesnakes, Indian mynah, Asian 

beauty snakes, coqui frogs, and small Indian mongoose. More 

importantly, WS made numerous specifi c recommendations 

for eliminating or minimizing these threats with fi ve key issues 

pertaining to all recommendations: funding, coordination and 

communication, education and training, control methods development, and enforcement. 

Ecology of Invasive Rose-Ringed Parakeets—Feral populations of rose-ringed parakeets have signifi cantly increased on 

the island of Kauai. Parakeet damage to kernels of corn cobs 

just prior to the harvest stage is especially serious. NWRC 

researchers completed a cooperative fi eld study with Pioneer 

Hi-Bred International Inc., to determine the rose-ringed parakeet population size, home range and dispersal patterns, roost 

locations, habitat use, food preferences, daily movements 

and associated crop damage. Parakeet exposure to diseases 

such as avian infl uenza, Newcastle’s disease,and avian psittacosis was also evaluated. NWRC researchers estimated 

the parakeet population to include more than 2,000 birds that 

ranged widely across the island to reach specifi c fi elds with 

seed farms. No diseases were detected in the birds sampled. 

NWRC researchers recommend damage management actions 

focus on specifi c agricultural fi elds and the birds’ potential 

nesting areas. 

Selected Publications:

BEARD, K. H. and W. C. PITT. 2012. Chapter 26: Caribbean 

tree frog (Eleutherodactylus coqui). Pp. 311-319. In: Handbook of Global Freshwater Invasive Species. Earthscan, 

London. Ed. Robert A. Francis (Invited Submission).

ENGEMAN R. M., W. C. PITT, A. R. BERENTSEN, and 

J. D. EISEMANN. 2012. Assessing spatial variation and overall density of aerially broadcast toxic bait during a rat eradication on Palmyra Atoll. Environmental Science and Pollution 

Research. DOI: 10.1007/s11356-012-1050-6.

MATHIES, T., W. C. PITT, and J. A. RABON. 2012. Boiga irregularis (Brown Treesnake) Diet. Herpetological 

Review. 43(1) 143-144.

OLSON, C., K. H. BEARD, and W. C. PITT. Biology and 

Impacts of Pacifi c Island Invasive Species: Eleutherodactylus 

planirostris, the greenhouse frog (Anura: Eleutherodactylidae). 

Pacifi c Science. 66:255-270.

PITT, W. C., L. C. DRISCOLL, and R. T. SUGIHARA. 2011. 

Effi cacy of rodenticide baits for the control of three invasive 

rodent species in Hawaii. Archives of Environmental Contamination and Toxicology 60(3): 533-542.

PITT, W. C., L. C. DRISCOLL, and E. A. VANDERWERF. 

2011. A rat-resistant artifi cial nest box for cavity-nesting birds. 

Human-Wildlife Interactions. 5:100-105.

The U.S.Department of Agriculture is an equal opportunity provider and employer
The U.S.Department of Agriculture is an equal opportunity provider and employer

Pitt, W. C., R. T. Sugihara, L. C. Driscoll, and D. S. Vice. 2011. 

Physical and behavioral abilities of commensal rodents related 

to design of selective rodenticide bait stations. International 

Journal of Pest Management 57:189-193.

PITT, W. C., M. HIGASHI, and T. M. PRIMUS. 2011.The effect 

of cooking on diphacinone residues in feral pig tissues. Journal 

of Food and Chemical Toxicology. 49:2030-2034.

PITT, W. C., K. H. BEARD, R. DORATT. 2012. Management 

of invasive coqui frog populations in Hawaii. Outlooks on Pest 

Management. 23(4): 166-169.

PITT, W. C., D. VICE, D. LUJAN, D. VICE, and G. WITMER. 

2012. Freeing islands from rodents: broadcast rodenticides help 

native species recover. Wildlife Professional 6: 33-34.

SHIELS, A.B. 2011. Frugivory by introduced black rats (Rattus 

rattus) promotes dispersal of invasive plant seeds. Biological 

Invasions 13: 781-792.

WALKER, L. R., and A. B. SHIELS. 2012. Landslide Ecology. 

Cambridge University Press, Cambridge, U.K.

Major Research Accomplishments:

 WS was an integral part of the largest environmental 

monitoring effort conducted in conjunction with a U.S. 

rodent eradication effort on Palmyra Atoll (a remote island 

in the Pacifi c Ocean, approximately 1,000 miles south of 

Hawaii).

 WS and a private engineering fi rm designed an automated 

aerial bait delivery system for use with the invasive brown 

treesnake.

 WS determined cooking had little effect on residual rodenticide concentrations in feral swine tissues from pigs 

exposed to rodenticide bait. Experts caution that the consumption of swine meat obtained from areas with active 

rodent control programs should be avoided. 

 WS developed a risk assessment and biosecurity plan for 

U.S. military operations in the Pacifi c. The assessment 

identifi ed possible routes of introductions for wildlife-related pathogens and invasive species.

 WS conducted a comprehensive study of invasive roseringed parakeet ecology and damage to agricultural crops 

in Hawaii.