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Blackbirds: Threat to Human Health?

Tuesday, April 2, 2002
filed under: Birds

Sunflower isn’t the only industry affected by blackbirds: These and other bird species are a problem for the livestock industry, and may be linked to the spread of E. Coli and other diseases that can affect humans.

Many sunflower growers have struggled for years with product theft—migrating blackbirds, grackles, and other wild birds that pluck ripened seeds from the sunflower heads in farmers’ fields. The problem can be so severe that it prevents some producers from growing sunflower, despite its viability as a cash crop.

These birds often prey upon livestock feedlots and dairies as well, becoming even more of a problem in winter, when snow cover makes open feed bunks and protection afforded by livestock shelters desirable habitat for bird flocks.

The economic loss to U.S. agriculture from bird populations is estimated at about $100 million annually, according to Wildlife Services, which is part of the U.S. Department of Agriculture's Animal and Plant Health Inspection Service.

Aside from the economic losses to bird feeding, there is also a concern about food safety: the role that birds may have as a vector in spreading diseases in livestock, some of which may be transmittable to humans.

“Our major concern with birds in feedlots is one, they can eat a lot of feed, and two, they may be carriers of so many different things,” says Wendy Peay, executive director of the Washington Cattle Feeders Association.

Cases of “mad cow” and food and mouth diseases in Europe that made newspaper headlines internationally has made the U.S. livestock industry more sensitive to food safety concerns. “The U.S. does not have foot and mouth disease, it has not had it for decades, but it is something we need to be concerned about, even with birds, since they could conceivably be carriers of that,” says Peay.

Starlings in particular are feedlot pests in Washington. “It’s a problem every feedlot deals with individually. But we do have control methods down where we know what works and what doesn’t,” says Peay. USDA Wildlife Services helps with bird control when needed.

Feedlots and dairies in other parts of the U.S. deal with bird problems too. “We have a real heavy load of birds, mostly starlings and grackles. It’s a seasonal problem, mostly in the fall. Certainly these pests can cause a wide variety of problems and we have a great interest in controlling it,” says Bas Aja, executive director of the Arizona Cattlemen’s Association.

Many feedlot operators already have bird and rodent control processes in place. “It’s just good animal husbandry,” says Gary Cowman, an animal nutritionist and executive director of research and technology services, for the National Cattlemen’s Beef Association.

Common control measures include enclosing open feeders, and using Starlicide avicide to suppress blackbird populations. Feedlot operators are understandably shy of discussing the bird control measures they use, however. While the public has no problem with poisoning mice and rats, poisoning birds can be a different story. One feedlot in central Washington made the papers, for example, when starlings that were poisoned there flew away and died, of all places, at a nearby cemetery.

Cowman, who coordinates the NCBA’s Beef Quality Assurance (BQA) program, says that, “without a doubt,” birds are a carrier of salmonella, but to what extent blackbirds and other species pose a threat in spreading this disease and other diseases to livestock and humans isn’t clear.

Gaining a better understanding of the host/pathogen relationship to aid in identifying potential pre-harvest critical control points and intervention strategies is the number one research priority of the Beef Industry Food Safety Council. BIFSCo ( was created by the beef industry to focus more attention on researching food safety issues.

Close to 40 companies and organizations representing all segments of the U.S. beef industry are involved in BIFSCo, including IBP, Monfort/ConAgra, Excel/Cargill, Burger King and McDonald’s.

In further defining its top research priority, BIFSCo aims within four years to “determine reservoirs for E. coli O157:H7 such as birds, rodents, other wildlife, bird droppings and other domestic animals and establish the distribution and survival in the environment, e.g., manure, soil, water, lagoons and feeds.”

Increasing Awareness of Birds as Disease Vector

Bob Bohlender, a North Platte, Neb., veterinarian, serves as chair of the NCBA’s animal disease research subcommittee, and on the advisory board of the organization’s BQA program. He says that some of the more uncommon diseases such as West Nile virus have raised awareness of birds as a vector in the spread of diseases. “It’s just one of the bio-security issues facing the livestock industry,” he says.

In 1999, a large die-off of American crows was implicated in a New York area epidemic of the WN virus. Through July 2001, more than 70 species of birds, mostly American crows, have tested positive for WN virus either by virus isolation or nucleic acid testing, according to The Centers for Disease Control and Prevention ( The most serious manifestation of WN virus infection is fatal encephalitis (inflammation of the brain) in humans and horses, as well as mortality in certain domestic and wild birds.

The issue of birds as a disease vector is broad, affected by different factors with no easy answers. For example, birds are able to travel many miles, and it’s possible that more desirable songbirds could be disease vectors too, along with the more pesky starlings and grackles, which Bohlender says are the primary problem birds that affect feedlots. Habitat, or lack thereof, can be a factor. He points out that ducks are becoming more of a problem in some livestock operations, pushed out of their preferred habitat by geese and sand hill cranes.

David Bergman, director of Arizona’s Wildlife Services office, says an informal survey of Wildlife Services state directors was conducted recently to get a better handle of bird issues affecting livestock, and how Wildlife Services can help manage bird problems.

The survey indicated that the primary pests in feedlots were, ranked in order: European starlings, cowbirds, blackbirds (red-winged, yellow headed, grackles), pigeons, house sparrows, ravens, and gulls.

For dairies, the primary pests were starlings, blackbirds, pigeons, cowbirds, house sparrows, and magpies.

The survey indicated that disease, feed loss, contamination, property damage, and production loss were the primary concerns of feedlots and dairies. Disease concerns mentioned that could be linked to birds included the West Nile Virus, histoplasmosis, cryptococcosis, bovine tuberculosis, foot and mouth disease, coccidiosis, and campylobactor.

Larry Clark, project leader for avian diseases and repellents for Wildlife Services in Ft. Collins, Colo., just completed a study on Canadian geese in New York, Wisconsin, Colorado, Washington, Oregon, and California. “We analyzed fecal samples for public health risk, and as one might expect, you do find toxicogenic bacteria of various sort.” About one-fourth of fecal samples contained some disease pathogens. E. coli and campylobactor were most prevalent, ranging between 8 and 15%.

“The bottom line is that bird fecal matter, in the case of Canadian geese, does have risks associated with it, and it could be a health issue,” says Clark.

Previous studies have been conducted on pigeons. “There is a lot of data, which shows that they are filthy beasts,” says Clark. Like geese, E. coli was the most prevalent disease found in pigeons.

There is limited data on blackbirds and starlings. Thus, Clark and other Wildlife Services officials are beginning a pilot survey this summer. “We’re going to pick a series of states and collect samples from livestock feed, birds, and cattle and look at where contamination might lie, then take the bacteria we get from these different sources and actually do DNA fingerprinting. For example, if we find the same clone of bacteria in cattle that we isolate from bird feces, then that’s pretty good evidence that either the cattle are giving it to birds, or vice versa.”

If a health risk is determined, then the study may be expanded to see if birds are transmitting diseases from one operation to another. “If disease risks are apparent, that this is a matter of herd health and human safety, and not just feed loss, that would change the economic balance of this issue considerably,” says Clark. – Tracy Sayler

A Dual Role as Protector and Eradicator

Wildlife Services (, part of the U.S. Department of Agriculture's Animal and Plant Health Inspection Service with a presence in all 50 states, plays a key role in blackbird control efforts in sunflower-producing states. WS assists in solving problems created when wildlife causes damage to agricultural, urban, or natural resources. WS also assists with wildlife problems involving threats to human health and safety, as well as threatened or endangered species.

WS balances the well-being of the public and wildlife, acting as a protective buffer, guarding not only resources, but also wildlife and the environment when conflicts between humans and wildlife occur. When formulating control strategies, WS specialists consider protected or endangered animals, environmental impacts, the cost effectiveness of control methods, and social and legal concerns. Control strategies may include the application of one or more techniques, and consideration is first given to nonlethal methods.

In all instances, WS programs are conducted to ensure no lasting negative impact on wildlife populations. One major aim of WS is educating the public and agricultural producers about the importance of using responsible strategies for living with wildlife.

A Pest and Safety Threat in Many Ways

Jennifer Lynch and Terry Messmer, wildlife experts at Utah State University, write in a bulletin on bird control management that “although starlings are generally more of a serious disease vector to livestock, they can also transmit a number of diseases to humans and other animals. Five bacterial diseases, two fungal diseases, four protozoan diseases, and six viral diseases may potentially be transmitted to humans and other animals by starlings.”

Histoplasmosis is a respiratory disease which humans can contract by breathing airborne fungal spores that originate in starling fecal matter, write Lynch and Messmer. In some rare cases, histoplasmosis has resulted in blindness and death in humans.

Starlings have been documented to transfer disease between livestock facilities, write Lynch and Messmer. In particular, hog operations can be significantly impacted by transmissible gastroenteritis virus (TGE). TGE can pass through the digestive tract of a starling and be spread to hogs through feces dropped on feeds.

Lynch and Messmer also point out that starling and blackbird fecal matter, noise and odor along with accumulations of droppings can create safety hazards in industrial structures, and that the acidity of bird droppings can corrode metals. They further point out that starling and other blackbird roosts located near airports may pose a serious threat to aircraft and airline safety. “Birds may potentially be ingested into jet engines, resulting in aircraft damage or loss and possibly human injury or death,” they write.

Starlings feed on fruit crops such as grapes, peaches, blueberries, strawberries, figs, apples and cherries, which can impact yields and damage produce quality, write Lynch and Messmer. Starlings may also compete for nesting sites with native nesting birds such as bluebirds, flickers and other woodpeckers, purple martins and wood ducks. They point to studies which have shown that starlings have significantly impacted local populations of other nesting species when nesting sites are limited.

Multiple Sources of E. coli Risk

Birds are certainly not the only potential source of E. coli O157 in feedlots and dairy farms. Dale Handcock, professor of veterinary sciences at Washington State University, says that feed, water troughs, and fecal contamination from other animals including horses, dogs, cats, and flies can be disease vectors.

Still, studies have been conducted which do implicate birds as a source of disease transmission. One study conducted in the Czech Republic indicated that black-headed gulls might play a role in the dispersal of pathogenic salmonella. Another study that looked at salmonella cases in Norway suggested an epidemiologic link between avian and human cases. “Having direct contact with wild birds or their droppings” was reported as one factor linked to an increased risk of infection.

A study in Germany also linked salmonella to soil samples contaminated with bird feces, mostly gulls and crows. The cases seemed to be greatest during autumn and winter, when a greater number of bird flocks congregated at contaminated sites. The study in Norway also observed a distinct seasonality, with 76% of recorded salmonella cases occurring between January and April.

Courtesy of Handcock, summaries of these studies and others, with references to published sources, can be found online at “Bird Disease Research Studies.”

Biocontrol Bird Repellent Available Again for Sunflower

BirdShield will be available to sunflower producers for a second year as a biodegradable, food-grade blackbird repellent. Its active ingredient is methyl anthranilate, a compound found in Concord and other grapes. The product, one of the first bio-control products in the marketplace, was approved for use on corn and sunflower by the Environmental Protection Agency last year.

Leonard Askham, BirdShield’s developer and a former animal control researcher at Washington State University, says between 80,000 and 120,000 acres of sunflower, both oils and confection, were treated between September and November last year. The vast majority of growers were satisfied with the product, which is aerially applied to the face of sunflower plant heads.

To be an effective deterrent to blackbird feeding, the product must land on the face of the sunflower head. As a sunflower plant starts to mature, the sunflower head starts to descend and even drop down into the canopy, which can make it more difficult to apply BirdShield. The National Sunflower Association is sponsoring research to find out why most applications were successful in getting product on these descending heads, and why some applications were unsuccessful.

Vern Hofman, extension ag engineer, North Dakota State University, will be conducting the BirdShield application research. Hofman will first determine if different water can prevent spray application from forming the proper particle size, and if so, what additives need to be added in order to make the correct particle size. Hofman will also focus on the aerial application technique. Nozzle size, type, angle and pressure will be tested for best coverage. Speed, altitude, time of day, temperature, humidity and any other factors that may affect the efficiency of the application process will also be studied.

Max Dietrich, the NSA’s production coordinator, believes this research will help increase knowledge about the best methods to apply the product. However, he points out that no product is ever 100% effective, and that farmers still need to use all bird deterrent tools available to them, such as the cattail spray program, cattail control management, Starlicide Complete, and scare tactics.

Birdshield can usually be tankmixed with insecticide, but Askham cautions that it should be premixed to test compatibility. Application timing is also crucial, he says. The product should be applied as soon as birds begin showing up in a field, and repeated as necessary to maintain repellency. “That’s about every seven to 10 days, but some growers said it lasted 10 to 12 days, and some confection growers said they only had to apply it once and it was good for three weeks. So again, producers should monitor their fields, and keep in mind that although this product has been proven effective, it’s not a silver bullet, and it’s not going to work in all cases.”

More information about the product can be found on the Internet, at – Tracy Sayler

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