United States Department of Agriculture

Animal and Plant Health Inspection Service

February 2011

In the United States, wildlife damage to 

agricultural resources is signifi cant. A 

survey conducted by the U.S. Department of 

Agriculture’s (USDA) National Agricultural 

Statistics Service (NASS) reported that 

wildlife damage to U.S. agriculture, including 

fi eld crops, vegetables, fruit, nuts, and 

livestock, totaled $944 million during 2001. 

According to other more recent studies, 

predators—such as coyotes, wolves, bears, 

and cougars—are responsible for more than 

$127 million in livestock losses annually; and 

the catfi sh aquaculture industry experiences 

nearly $25 million in losses annually due to 

cormorants alone.

The USDA Animal and Plant Health Inspection 

Service’s Wildlife Services (WS) program 

provides Federal leadership and expertise to 

help reduce wildlife damage to the food crop, 

livestock, and aquaculture industries. The 

National Wildlife Research Center (NWRC) 

is the research arm of the WS program. Its 

scientists develop new tools and techniques 

for reducing wildlife damage to agriculture.

Protecting 

Agriculture

Food Crops

Birds cause severe damage to 

a variety of agricultural crops, 

including sunfl owers, rice, corn, 

winter wheat, fruits, and nuts. Field 

crops are especially vulnerable to 

bird damage as they serve as a 

“buffet” for migrating birds providing 

a high-energy, relatively easy food 

source.

 

 Sunfl ower and rice crops are a 

favorite of blackbirds, sustaining 

yearly losses of $5–13 million. 

Discouraging blackbirds from 

foraging in favored sunfl ower fi elds 

is diffi cult; however, repellents can 

be effective if alternative foraging 

sites are readily available. NWRC 

scientists recently completed 

effi cacy studies in which blackbirds 

were offered oilseed and 

confectionary sunfl ower treated with 

an anthraquinone-based repellent. 

Compared to untreated fi eld sites, 

scientists observed less sunfl ower 

damage and more sunfl ower yield 

within confectionary sunfl ower 

fi elds treated with the repellent. 

Though the anthraquinone-based 

repellent proved effective, additional 

fi eld studies are needed to identify 

practical and effective methods for 

applying the repellent to ripening 

sunfl ower heads. 

 Other successful NWRC 

methods for reducing blackbird 

damage include the application 

of a registered cattail herbicide 

to reduce blackbird roosting sites 

and the establishment of wildlife 

conservation sunfl ower plots. Cattail 

marshes located next to sunfl ower 

fi elds create perfect roosting 

sites for blackbirds. By thinning 

select marshes with the herbicide 

glyphosate, WS biologists make 

these roosts less attractive, thus 

dispersing large concentrations of 

blackbirds away from sunfl ower 

production areas. Wildlife 

conservation sunfl ower plots (or lure 

crops) involve planting a small fi eld 

of sunfl ower or other crop to attract 

the birds away from the commercial 

sunfl ower fi eld. The goal is to keep 

the birds in the lure crop as long as 

possible to reduce the time spent in 

nearby commercial sunfl ower fi elds. 

Abundant red-winged blackbirds often feed 

on sunfl ower crops in the Midwest. 

(Photo by APHIS–WS–NWRC)
Farmers can continue to spray 

registered repellents and harass 

birds in their commercial fi elds to 

encourage the birds to feed in the 

lure crops. 

 Rodents continue to impact 

crop production and livelihoods of 

farmers in the United States and 

around the world. Roof, Norway, 

and Polynesian rats, voles, and 

other rodents cause damage to 

seed (i.e., corn, rice, and soybean), 

vegetable, and fruit crops. They 

directly consume plants, cause 

product blemishes that result in a 

loss of market quality, and enable 

secondary infections by insects and 

disease. Chemical approaches, like 

rodenticides and other toxicants, 

are important tools for reducing 

damage; however, they can pose 

hazards to non-target animals and 

the environment. 

 

NWRC works to reduce or eliminate 

these hazards, as well as develop 

and register effective, alternative 

approaches for managing wildlife 

damage. For example, NWRC 

researchers found that adding 

an anthraquinone repellent to 

rodenticide baits successfully 

reduces consumption of the baits 

by Canada geese and ring-necked 

pheasants. These fi ndings could 

aid in the development of new 

bait formulations that reduce the 

ingestion of rodenticides by these 

and other non-target wildlife species. 

 Free-ranging populations of feral 

swine (also called wild pigs) exist in 

at least 39 states. Some experts 

estimate the number of feral swine 

in the United States at more than 4 

million, with the largest populations 

located in California, Florida, Hawaii, 

and Texas. Foraging, rooting, 

digging, and trampling by feral 

swine in pastures and agriculture 

crops result in millions of dollars in 

damages each year in the United 

States. Feral swine are also effi cient 

predators of young livestock and 

other small animals, and transmit 

disease to domestic livestock. 

NWRC scientists are studying the 

potential costs associated with E. coli 

contaminations to vegetable crops 

caused by feral swine. 

 

Developing effective methods and 

tools for managing feral swine 

populations is essential to protect 

agriculture and livestock from feral 

swine damage. NWRC scientists are 

evaluating fencing to prevent feral 

swine damage and to quickly contain 

feral swine during disease outbreaks. 

Scientists are also evaluating feeders 

specifi cally for feral swine to deliver 

vaccines or toxicants. 

Livestock

The development of new tools 

to reduce livestock predation 

and to protect public safety is a 

high priority for the WS program. 

Livestock predation costs producers 

approximately $127 million 

each year. NWRC uses a multidisciplinary approach to study 

Voles eat out the lower, fl eshy “heart” 

of the artichoke vegetable, making 

them unmarketable. (Photo by 

APHIS–WS–NWRC)

Invasive feral swine impact resources 

through their destructive feeding 

behavior, competition with native 

wildlife, and impacts to domestic 

animal agriculture. (Photo by 

APHIS–WS–NWRC)
predator ecology and the impact 

of predators and predator removal 

on ecosystems. Such studies 

are fundamental to conducting 

responsible predator management. 

In addition, NWRC researchers also: 

investigate alternative, nonlethal 

tools and techniques to reduce 

livestock predation; research 

improved methods for capturing 

predators and for monitoring their 

behaviors and movements; and 

develop more selective lethal 

management techniques. 

 In fi eld studies, NWRC 

researchers demonstrated that 

surgical sterilization of alpha 

(dominant) coyotes reduced 

sheep predation by an average of 

87 percent relative to predation 

by non-sterilized coyotes. The 

sterilized coyotes continued to 

maintain territories and pair bonds 

similar to non-sterilized coyotes. In 

subsequent computer simulation 

models, the sterilization of coyotes 

(regardless of sex or social status) 

appeared to offer the largest and 

most lasting impact on coyote 

populations compared to more 

traditional management strategies. 

Scientists hypothesized that 

sterilized coyotes are less likely to kill 

livestock because they do not have 

the increased energy requirements 

associated with producing, feeding 

and rearing pups. Although 

sterilization is initially labor and cost 

intensive as a management tool, it 

may be an economically feasible 

option for coyotes in certain areas 

because of the long-lasting effects of 

reduced livestock predation.

 Livestock producers are often 

confronted with the challenge 

of reducing the transmission of 

diseases from wildlife to livestock. 

For example, in the Great Lakes 

Region of the United States, whitetailed deer have served as a wildlife 

reservoir for the disease bovine 

tuberculosis. Bovine tuberculosis 

is a contagious, bacterial disease 

that leads to weight loss and death 

in cattle and deer. In 2008, 

NWRC scientists and collaborators 

evaluated the effectiveness of 

livestock protection dogs (LPDs) for 

excluding white-tailed deer from 

livestock pastures. The fi ndings 

showed LPDs are particularly 

effective at protecting cattle and 

concentrated cattle feed from deer. 

Data showed only 3 cases where 

deer came within 5 meters of cattle 

in protected pastures compared to 

79 cases in unprotected pastures. 

Based on observation data, total 

time spent by deer in LDP-protected 

pastures was far less (5 minutes) 

compared to unprotected pastures 

(425 minutes). Researchers also 

recorded only 2 events where 

deer consumed hay in protected 

pastures, compared to 303 events in 

unprotected pastures. The results 

support that LPDs may reduce 

potential for disease transmission 

from deer to cattle in small pasture 

settings. 

Aquaculture

In the past 30 years, populations 

of fi sh-eating birds, such as 

cormorants, herons, and pelicans, 

have increased dramatically, 

causing substantial economic 

impacts to aquaculture production 

in the southeastern United States. 

For the aquaculture industry, 

the costs associated with bird 

In an effort to reduce disease 

transmission between deer and livestock, 

NWRC researchers investigated the use 

of livestock protection dogs to keep deer 

away from cattle feed and water sources. 

(Photo by APHIS–WS–NWRC)
During the study, between 1,347 

and 1,775 metric tons of catfi sh 

were consumed by cormorants 

in the Delta region of Mississippi, 

resulting in losses to the catfi sh 

industry of $10.3 to $13.7 million 

annually.

 In collaboration with university 

parasitologists at Mississippi 

State University, NWRC scientists 

described the life cycle of the 

species of trematode infecting 

catfi sh in the southeastern United 

States and confi rmed that American 

white pelicans serve as host for 

this parasite. The trematode has 

been estimated to cause as much 

as a 10 percent annual economic 

loss to the catfi sh industry. This 

research demonstrated that 

American white pelicans can 

transmit this disease among catfi sh 

ponds, but that double-crested 

cormorants, great blue herons, 

and great egrets did not appear to 

serve as hosts for this trematode. 

NWRC scientists also identifi ed an 

introduced species of snail that 

is an intermediate host for the 

parasite. These studies underscore 

the importance of preventing 

pelican use of aquaculture facilities 

and understanding the biology 

and epidemiology of the disease 

organism to aid in treatment and 

prevention.

damage and damage prevention 

are conservatively in the tens of 

millions of dollars annually. NWRC’s 

research helps to determine 

the impact of fi sh-eating birds 

on aquaculture production and 

to develop methods to reduce 

depredation of southeastern catfi sh, 

baitfi sh, and crawfi sh industries. 

Current NWRC research is aimed 

at gaining information about the 

abundance, distribution, and 

foraging behavior of fi sh-eating birds, 

the economic impacts associated 

with their foraging activities, and 

the diseases they transmit at 

aquaculture facilities. 

 Recent NWRC studies 

documented that cormorants use 

catfi sh ponds extensively during 

January through April each year, 

with the greatest economic damage 

occurring in February and March. 

Additional Information

For more information, please contact:

National Wildlife Research Center

USDA, APHIS, WS

4101 LaPorte Avenue

Fort Collins, CO 80521

You may also call NWRC at 

(970) 266-6000 or visit our Web site at 

http://www.aphis.usda.gov/wildlife_

damage/nwrc/.

The U.S. Department of Agriculture (USDA) prohibits 

discrimination in all its programs and activities on the 

basis of race, color, national origin, sex, religion, age, 

disability, political beliefs, sexual orientation, or marital 

or family status. (Not all prohibited bases apply to 

all programs.) Persons with disabilities who require 

alternative means for communication of program 

information (Braille, large print, audiotape, etc.) should 

contact USDA’s TARGET Center at (202) 720-2600 

(voice and TDD). 

To fi le a complaint of discrimination, write USDA, 

Director, Offi ce of Civil Rights, Room 326-W, 

Whitten Building, 1400 Independence Avenue, SW, 

Washington, DC 20250-9410 or call (202) 720-5964 

(voice and TDD). USDA is an equal opportunity 

provider and employer. NWRC’s research helps to determine the 

impact of fi sh-eating birds on aquaculture 

production and to develop methods to 

reduce depredation of catfi sh, baitfi sh, and 

crawfi sh industries. (Photo by NASA)