Contact Information: 

Dr. George Linz 

Supervisory Research Wildlife Biologist

North Dakota Field Station

2110 Miriam Circle, Suite B

Bismarck, ND 58105

Phone: (701) 250-4469 

FAX: (701) 250-4408

george.m.linz@aphis.usda.gov

www.aphis.usda.gov/wildlife_damage/

nwrc/ 

Major Cooperators

• Gowan Company

• Kansas Feedlot Association

• Louisiana Blackbird Committee

• Louisiana Rice Producers Association

• Louisiana Rice Research Board

• Louisiana State University, Louisiana 

Rice Research Station

• Michigan State University

• Missouri Rice Research and Merchandising Council

• National Sunfl ower Association 

• North Dakota State University

• North Dakota Department of Agriculture

• Ohio Dairy Association

• Ohio State University

• Syngenta Crop Protection

• USA Rice Federation

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 Address the Concerns of 

Farmers, and Feedlot, Dairy and Urban Area Managers

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

research organization 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 Bismarck, North Dakota, evaluates and 

develops methods for managing national blackbird damage to sunfl ower, rice, and corn 

in the Great Plains. The fi eld station also leads research on national problems involving 

bird damage to fruit crops; Canada goose damage to sprouting crops; European starling 

damage and diseases in urban areas, feedlots and dairies; and woodpecker damage to 

utility structures and buildings.

Blackbirds and European starlings damage grain crops and eat livestock feed, resulting in 

signifi cant economic losses to agricultural producers. Cedar waxwings and robins damage 

blueberries, cherries, grapes, and apples causing millions of dollars in damage to these 

high-value crops. NWRC scientists are studying ways to refi ne current damage abatement 

methods and develop new methods for reducing damage. Additionally, researchers are 

looking for nonlethal methods to expand capabilities to target specifi c problem-causing 

birds. Red-winged blackbirds, common grackles, yellow-headed blackbirds, and brownheaded cowbirds cause an estimated $20 million worth of damage to newly planted and 

ripening rice in Arkansas, California, Louisiana, Missouri, and Texas; $15 million worth of 

sunfl ower in North Dakota and South Dakota; and $35 million worth of ripening and newlyplanted corn nationally. Some individual rice and sunfl ower growers report 100 percent 

losses due to bird depredation. Birds, especially European starlings, cedar waxwings, 

and robins, cause $41 million in damage in the leading fruit growing states of California, 

Michigan, New Jersey, New York, North Carolina, Pennsylvania, and Washington.

NWRC scientists routinely work with producers, commodity groups, research boards, 

universities, and local, State and Federal agencies to develop safer and more effective 

methods to reduce bird depredation on seeded and ripening sunfl ower, corn, rice, and 

fruit crops to improve profi tability for growers. To develop new methods and tools, NWRC 

scientists conduct multifaceted studies involving the use of both captive and free-ranging 

birds to determine the status of blackbird populations in the sunfl ower-, corn- and ricegrowing states and fruit-eating birds in apple-, grape-, blueberry- and cherry-growing 

states; estimate the economic impacts of birds on the crops; evaluate and develop 

nonlethal repellants for deterring birds; and improve the effectiveness and safety of 

avicides for reducing depredating populations. 

Applying Science and Expertise to Wildlife Challenges

Blackbird Population Management Modeling—DRC-1339 is a slow-acting avicide used 

to reduce local populations of European starlings, blackbirds and other birds. It is diffi cult to 

accurately estimate the number of birds killed with DRC-1339 because carcass searches 

and other types of counts are not accurate predictors of take at staging area bait sites. 

To improve mortality estimates associated with current linear models and DRC-1339 use, 

NWRC scientists developed a semi-mechanistic model that combines mechanistic modeling of environmental and biophysical processes with statistical modeling of DRC-1339 toxicities, avian physical and physiological traits, and foraging behavior. The scientists used 

simulated baiting scenarios in Missouri and Louisiana to compare take between the two 

models. Compared to the linear model, the semi-mechanistic model estimates ranged from 

Reducing Blackbird and Starling educing Blackbird and Starling 

Conflicts

Groups Affected By These Problems

• Consumers and producers of 

sunfl ower, rice, corn, diary, meat, 

and other products 

• Feedlot Owners Association

• National and State Fruit Grower 

Associations

• National Sunfl ower Association 

• North Dakota Department of 

Agriculture

• North Dakota Game and Fish 

Department

• Processors, manufacturers, suppliers, and sellers of sunfl ower, rice, 

fruit, corn, dairy, and meat

• South Dakota Department of 

Agriculture

• South Dakota Game, Fish and Parks

• South Dakota Oilseed Council

• Utility companies
5 percent higher to 59 percent lower, depending on the species 

and gender compositions of the blackbird fl ocks. On average, 

the new model’s estimates were 24 percent lower than the linear 

model. Unlike the linear model, the new model accounts for the 

effects of meteorological and environmental conditions that likely 

infl uence feeding rates at DRC-1339 bait sites. NWRC researchers believe that the semi-mechanistic model represents a more 

scientifi cally rigorous approach than the linear model toward estimating take that can be applied to all staging area bait applications regardless of region or time of year.

European Starlings’ Role in the Spread of Salmonella—

Characterizing and mitigating diseases introduced by wildlife 

to concentrated animal feeding operations (CAFO) can reduce 

the spread of microorganisms throughout the environment 

while increasing agricultural productivity. To better understand 

the disease risks associated with bird use of CAFO, NWRC 

scientists assessed the capacity of European starlings to 

spread Salmonella enterica to cattle, their feed, and water. 

Scientists found that Salmonella enterica contamination of cattle 

feed troughs and water troughs increased as more starlings 

entered feed troughs, indicating that starlings are a source 

of S. enterica contamination in CAFO. Thus, employment of 

starling management tools such as population control, habitat 

management, exclusionary devices, and bird repellants may 

reduce the amplifi cation and spread of this disease within 

livestock production systems. 

Ultraviolet Cues Used in Blackbird Food Selection—

Although it has long been known that birds use ultraviolet (UV) 

wavelengths for mate selection, researchers have now learned 

that UV wavelengths also infl uence bird feeding behavior 

and food selection. While UV wavelengths are invisible to 

humans, NWRC researchers found that birds exposed to an 

UV-absorbent, post-ingestive repellent subsequently avoided 

UV-absorbent and UV-refl ective food. In studies with captive 

red-winged blackbirds, researchers learned that blackbirds shift 

preferences for both familiar and unfamiliar fl avors based on 

their feeding experiences and rely on visual cues to avoid food 

previously paired with negative consequences. The researchers 

hope to use these fi ndings to improve our understanding and 

management of bird damage to agriculture.

European Starlings May Move Pathogens Among Feedlots—

NWRC and North Dakota State University scientists monitored 

site use and movements of European starlings during the winter 

at two concentrated animal feeding operations (CAFO) in central 

Kansas. Their research investigated the possible role of starlings 

in pathogen transmission at CAFO. Few birds (9 percent) moved 

between feedlots. Starlings rarely completely abandoned the 

feedlot where they were fi rst captured, but 40 percent of the 

birds temporarily visited other feedlots. The furthest distance a 

bird was detected from its original capture site was 42 miles/68 

kilometers. Scientists speculate that the limited frequency of time 

spent at non-capture-site feedlots may lower, but not eliminate, 

the potential risk of starlings spreading pathogens among 

feedlots. Researchers still recommend management strategies 

to reduce starling populations within feedlots and, thereby, 

the subsequent risk of the birds spreading pathogens to other 

feedlots.

Anthraquinone to Alleviate Non-Target Take From Rodenticides—Rodenticides, such as zinc phosphide, are often 

used to control rodent populations that cause damage in croplands and rangelands. Zinc phosphide breaks down rapidly 

after ingestion and poses little risk to predators and scavengers that might consume treated rodents; however, birds that 

directly consume the rodenticide bait may be at risk. In an effort to reduce nontarget hazards to birds during rodent control 

efforts, NWRC researchers evaluated whether the addition 

of the registered goose repellent anthraquinone to rodenticide baits would prevent consumption of the baits by certain 

birds. Anthraquinone, which occurs naturally in some plants, 

produces a laxative effect when eaten. In addition, anthraquinone absorbs near-ultraviolet light that is visible to most birds. 

This color cue may facilitate the repellency effect in birds. In 

studies involving captive birds, NWRC researchers treated 2 

percent zinc phosphide baits typically used in rodenticide applications with 2 to 2.5 percent anthraquinone (Arkion® Life 

Sciences). No mortality or signs of zinc phosphide toxicosis 

were observed among the 20 Canada geese, 24 horned larks, 

and 47 ring-necked pheasants that were offered the repellenttreated zinc phosphide baits. Although some geese and 

pheasants initially sampled treated baits, all birds survived and 

subsequently avoided treated baits throughout the remainder 

of the study. However, anthraquinone may affect consumption 

of repellent-treated rodenticide baits by target species such as 

black-tailed prairie dogs. Supplemental performance testing 

and fi eld effi cacy studies are necessary for further development of a combined bird-repellent rodenticide bait.

Selected Publications:

CARLSON, J. C., A. B. FRANKLIN, D. R. HYATT, S. E. 

PETTIT, and G. M. LINZ. 2011. The role of starlings in the 

spread of Salmonella within concentrated animal feeding 

operations. J. Applied Ecology 48:479–486.

FORCEY, G. M., W. E. THOGMARTIN, G. M. LINZ, and W. J. 

BLEIER. 2011. Land use and climate infl uences on waterbirds 

in the prairie potholes. Journal of Biogeography 38:1694–

1707. 

GAUKLER, S. M., H. J. HOMAN, G. M. LINZ, and W. J. 

BLEIER. 2012. Use of feedlots and roost sites by radio-tagged 

European starlings. Human-Wildlife Interactions 6:30–37. 

HOMAN, H. J., R. S. STAHL, and G. M. LINZ. 2013. 

Comparison of two models for estimating mortality from 

baitings with Compound DRC-1339 Concentrate avicide. Crop 

Protection 45:1-5. 

LINZ, G. M., J. B. WINTER, and W. J. BLEIER. 2012. 

Evaluation of elevated bait trays for attracting blackbirds 

(Icteridae) in North Dakota. Crop Protection 41:30–34.

WERNER, S. J., S. K. TUPPER, J. C. CARLSON, S. E. 

PETTIT, J. W. ELLIS, and G. M. LINZ. 2012. The role of 

a generalized ultraviolet cue for blackbird food selection. 

Physiology & Animal Behavior 106:597–601.

The U.S. Department of Agriculture is an equal opportunity employment provider and employer
WERNER, S., S. K. TUPPER, S. E. PETTIT, J. C. CARLSON, 

and G. M. LINZ. 2011. Anthraquinone repellent to reduce nontarget take of non-target birds from zinc phosphide rodenticide 

applications. Applied Animal Behavior Science 135:146–153. 

WERNER, S. J., G. M. LINZ, J. C. CARLSON, S. E. PETTIT, S. 

K. TUPPER, and M. M. SANTAR. 2011. Anthraquinone-based 

bird repellent for sunfl ower crops. Applied Animal Behaviour 

Science 129:162–169. 

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

Major Research Accomplishments:

 WS research discovered that ultra-violet vision in 

birds was important for food selection and could 

be used in the development of bird repellents to 

protect crops.

 WS developed a model to estimate the avicide 

DRC-1339’s effectiveness and impact on blackbird 

populations. 

 WS determined that combining anthraquinone with 

rodenticide bait helps to prevent the consumption 

of bait by non-target bird species, such as Canada 

geese, ring-necked pheasants,and horned larks. 

 WS and North Dakota State University scientists 

found that managing starling populations might be 

a strategy for reducing the spread of disease within 

livestock production systems.