42. Take precautions to keep your feeder birds safe from toxins and diseases.

Redpolls and siskins

When I was rehabilitating wild birds, I sometimes got phone calls from anxious people who had sick or dying birds in their yards. In one case, the caller later learned that her birdseed was contaminated, and many other people who had purchased seed from the same supplier had also lost birds. Another caller’s feeding station apparently became infected with botulism during a very wet spring. In both cases, the people felt devastated about hurting the birds that they were trying to help.

To maximize the advantages and minimize the potential harm of bird feeding for individual birds and local populations, it’s important to take some basic precautions. Here are a few guidelines to prevent bird diseases at feeding stations:

There are a few dangerous organisms that can hurt backyard birds. None of the diseases they cause, except House Finch conjunctivitis, is commonly seen at feeders, but knowing what to look for and how to prevent outbreaks or transmission will help you avoid sad situations.

1. Aflatoxins.

Birdseed, especially corn and peanuts sold specifically for bird feeding, can be contaminated with aflatoxins. These poisons are produced by two fungi that are common and widespread in nature, Aspergillus parasiticus and Aspergillus flavus, which grow most rapidly in warm and humid environments. Aflatoxins are highly dangerous for humans and livestock, so seed sold for human consumption and animal feed is screened by the U.S. Department of Agriculture. Seed sold for bird feeding isn’t legally required to be screened, and some seed sold for this purpose may not be. Research conducted by Dr. Scott Henke of Texas A&M University found that 17 percent of birdseed samples tested in Texas contained relatively large amounts of the toxin and that feeding birds contaminated seed can be very harmful. Consumers should demand that seed purchased for bird feeding be screened for this dangerous toxin.

Steller's Jay

Aflatoxins develop most easily in seeds packaged in plastic bags, because condensing moisture fosters fungal growth. To avoid this, don’t buy corn in non-breathable plastic bags. Make sure it’s fresh; store it in a clean, dry place; and keep your feeders and the ground beneath them meticulously clean. Choose peanuts sold for human consumption.

2. Aspergillosis.

Aspergillosis is another fungal disease that is usually caused by Aspergillus fumigatus, which is commonly found in decaying vegetable matter, including moldy birdseed. A bird becomes infected by eating or inhaling mold spores from contaminated foods. The fungus produces lesions in the lungs and air sacs, causing difficulty breathing, emaciation, and excessive thirst. Birds often appear to have difficulty walking. When their eyes are infected, there may be a white opacity accompanied by a discharge. Healthy birds normally resist the disease, but birds with depressed immune systems are especially vulnerable. Occasionally, outbreaks of the disease cause significant mortality in certain species. Aspergillosis outbreaks at feeders are preventable by keeping feeders clean, the ground beneath them well raked, and spoiled seeds and shells well covered where you dispose of them (preferably in a screened compost bin).

3. Avian pox.

Birds don’t get chickenpox, but they do get two forms of avian pox. (Oddly, chickenpox most likely got its name because it isn’t particularly dangerous, so it was considered more “chicken” than the similar but deadly smallpox.) In the more common form of avian pox, wartlike growths appear on the featherless areas of the body around the eye, at the base of the beak, and on the legs and feet. When limited to the eye areas, the disease may be mistaken for conjunctivitis. In the rarer form, plaques develop on the mucous membrane of the mouth, throat, trachea, and lungs. These make breathing and feeding difficult and increase susceptibility to secondary infections, which kill the bird.

Wild Turkey

Avian pox can be caused by several strains of poxviruses and has been reported in at least sixty species of birds from twenty families, including turkeys, hawks, owls, and sparrows. The virus can be spread by direct contact with infected birds of contact with contaminated surfaces or through contaminated food or water. If you see a bird that may be infected with avian pox, it’s a good idea to close down the feeding station for a week or two and make sure that the ground is raked and feeders are cleaned before resuming feeding.

4. Bird flu.

Bird flu occurs on overcrowded, unsanitary poultry farms. According to the Centers for Disease Control and Prevention:

Type A influenza viruses can infect several animal species, including birds, pigs, horses, seals and whales. Influenza viruses that infect birds are called “avian influenza viruses.” Birds are an especially important species because all known subtypes of influenza A viruses circulate among wild birds, which are considered the natural hosts for influenza A viruses. Avian influenza viruses do not usually directly infect humans or circulate among humans.

Influenza A viruses can be divided into subtypes on the basis of their surface proteins—hemagglutinin (HA) and neuraminidase (NA). There are 15 known H subtypes. While all subtypes can be found in birds, only 3 subtypes of HA (H1, H2 and H3) and two subtypes of NA (N1 and N2) are known to have circulated widely in humans.

Avian influenza usually does not make wild birds sick, but can make domesticated birds very sick and kill them. Avian influenza A viruses do not usually infect humans; however, several instances of human infections and outbreaks have been reported since 1997. When such infections occur, public health authorities monitor the situation closely because of concerns about the potential for more widespread infection in the human population.


[*This information needs to be updated–it was true as of publication in 2006, but many more wild birds have been found carrying bird flu.] Since 1997, only one wild bird in the United States has tested positive for avian flu, a Peregrine Falcon. People have contracted the disease from contact with infected poultry and from other humans. Intensive production practices foster conditions in which bird flue and other diseases flourish. Overcrowded birds are more stressed, and cruel practices such as debeaking add to their stress level, making them far more vulnerable to illness. The excessive use of antibiotics also contributes to their stress level and, dangerously, to the virulence of bacterial diseases, making the birds more susceptible to viral infections due to their weakened immunity. In the final analysis, the probability of contracting bird flu from other people or from mass-produced grocery store poultry is greater than the chance of contracting it from wild birds. There is no known connection between bird flu and bird feeding. At this time, the best thing we can do to protect ourselves from bird flu is to buy organic, free-range poultry from a trusted local grower.

5. Conjunctivitis.

Mycoplasmal conjunctivitis is an eye disease limited mostly to House Finches and, to a lesser extent, American Goldfinches, predominantly in the eastern half of the country. The eastern population of House Finches was introduced from a handful of individuals released in New York in the 1940s, so these birds are fairly closely related to one another. Apparently, most of the eastern birds are genetically susceptible to this disease. Infected birds may have red, swollen, runny, or crusty eyes. In the worst cases, the eye becomes swollen shut or crusted over, leading to blindness. Infected birds may sit quietly, their feathers puffed out a bit, scratching one eye with a foot or against a tree. Although some infected birds recover, most probably die from starvation, exposure, or predation.

House Finch

Many people associate this disease with bird feeding because so many of the sick birds are detected at feeding stations, but House Finches are flocking birds whether at feeders or away from them. According to the Cornell Lab, the worst period of disease transmission is late summer and fall, when House Finches visit feeders only sporadically, Disease prevalence is lowest during midwinter, when finches visit feeders much more regularly. And the epidemic did not affect any native eastern bird species common at bird feeders during the period that it reduced the eastern House Finch population by 60 percent. The disease took several years to reach the western population and (as of this writing) has infected comparatively few western House Finches. In the West, where the species is native and abundant, including at feeders, the House Finch population is more genetically diverse and at least somewhat resistant to the disease.

If you detect an infected bird using a tube feeder with a design that requires it to turn the side of its face toward the feeder, take the feeder down, clean it thoroughly, and don’t put it back out while infected birds are visiting. As with other bird diseases, if you notice any sick or dying birds in your yard, it’s a good idea to close down your feeding station entirely for at least a week. Make sure you report any infected birds to the Cornell Lab’s House Finch and American Goldfinch Disease Survey.

6. Salmonella.

Salmonellosis, or salmonella poisoning, is caused by bacteria belonging to the genus Salmonella and is a common cause of mortality in birds. Although it is found more often in natural settings than in backyards, feeder birds can be infected, and unfortunately, the symptoms are not always obvious. As with most sick birds, those suffering from salmonellosis may appear fluffed up and depressed. They may also have swollen eyelids, and the feathers near the vent may be stained and pasty. They are often lethargic and easy to approach. Unfortunately, some infected birds not yet showing outward signs of illness can spread the infection to other birds via their droppings.

Salmonellosis is transmitted primarily from bird to bird by fecal contamination of food and water, although it can also be transmitted by ingestion of contaminated feed or from physical contact. The disease can cause significant mortality. If you notice a bird that may be suffering from salmonellosis, it’s important to close down your feeding station and birdbath for a couple of weeks. Rake all areas where birds have been gathering, and clean all feeders thoroughly. The original infection probably arose elsewhere, but it’s important to prevent it from spreading to other birds. Ground-feeding birds are particularly susceptible to salmonellosis, so make sure that you rake frequently.

7. Trichomoniasis.

Trichomoniasis is a disease cause by the protozoan Trichomonas gallinae. It most commonly affects pigeons and doves and the predators that feed on them, but it can also spread to feeder birds when infected doves are present. This disease is characterized by raised lesions in the mouth, esophagus, and crop, so an infected bird may have trouble closing its mouth. The disease may be present in the mouth secretions of birds that appear to be healthy but are carriers, especially pigeons. The oral secretions of infected birds can contaminate feeders, the ground beneath feeders, and birdbaths, which can in turn expose many other birds to the disease. Mortality from this disease varies but can be quite high. Changing birdbath water frequently and raking beneath feeders will protect your birds from this disease. Discouraging pigeons from gathering at your feeding station can be an important preventive measure.

8. West Nile virus.

This disease, spread by mosquitoes, biting flies, and possibly other blood-sucking parasites, is highly lethal to horses and many species of birds, especially jays and crows. Less than 1 percent of humans bitten by mosquitoes harboring West Nile virus get seriously ill, but for this 1 percent, the disease can be extremely serious. It affects the brain similar to encephalitis and can cause permanent neurological damage; it’s fatal in 3 to 15 percent of serious cases (that is, in 0.03 to 0.15 percent of people exposed to the virus). The disease is most dangerous for the elderly and those with compromised immune systems, who must be protected from mosquito birds. Fortunately, the vast majority of people bitten by infected mosquitoes do not get sick or have only mild symptoms. In contrast, 99 to 100 percent of crows exposed to the virus in laboratory tests died. And West Nile virus seems to kill infected birds very quickly.


To prevent the disease in the first place, it’s important to refresh your birdbath every few days, keep gutters cleaned, and eliminate any other sources of stagnant water to deter mosquito breeding. West Nile virus is most frequently transmitted by mosquitoes belonging to the genus Culex—the mosquitoes most closely associated with human habitation.

If you find a bird that may have died from West Nile virus, wear gloves when you pick it up and double-bag it in plastic. Then call the county health department to find out whether it is testing birds to verify the presence of the disease in your area. Testing is expensive, so if the authorities are already aware of the presence of the disease in your area, they may not want the carcass. In that case, keep it double bagged and dispose of it in the trash to prevent further disease transmission.

What should you do if you notice a diseased bird at your feeding station? According to the Cornell Lab:

Only veterinarians or federally licensed wildlife rehabilitators can legally treat wild birds. Therefore, if you find a diseased bird, it’s best to report it to your state or local wildlife agency. If you are advised to take the bird in for an examination, try to catch the bird by throwing a light towel over it and placing it in a box with air-holes. If you find a dead bird, place it in a double plastic bag and into the garbage (wear gloves).

If a sick bird comes to your feeder, minimize the risk of infecting other birds by cleaning your feeder area thoroughly. If you see several diseased birds, take down all your feeders for at least a week to give the birds a chance to disperse. Keep the feeders down until you no longer see diseased individuals. And remember that prevention is the key to avoiding the spread of disease. Regularly clean your feeders even when there are no signs of disease and prevent overcrowding by adding more feeders or setting up different types of feeders that allow only a few birds to visit at one time. And store your seed where it will remain as cool and dry as possible.

9. Pesticide poisoning.

Pesticide poisoning often affects backyard birds, especially within two or three days of pesticide applications. An affected bird may be disoriented or have trouble balancing. It may be lying on its side, unable to sit at all. Although many lawn chemicals break down into less toxic substances within a few days, the damage they do to birds during their most toxic period is usually permanent and often fatal.

I once cared for a newly fledged Blue Jay that a woman had seen hopping in her neighbor’s freshly sprayed lawn. Hours later when she looked out, the little jay was lying helplessly on his side, unable to move. When she brought him to me, I examined him closely and found no injuries whatsoever, although his belly feathers were sticky and bore a faint odor. His eyes were bright, and he opened his mouth to beg, so I fed him several times that day. His digestive processes were fine, but he had very little muscular control and could not balance himself. I continued to feed him and fashioned a little sling from some handkerchiefs so that I could carry him with me during my daily activities to ensure that he stayed upright and was getting enough mental stimulation; at night I put him in a plastic bucket lined with paper towels to prop him up. I’d never done physical therapy on a bird and didn’t know anyone who had, but each day I’d open and close his wings and move his legs to keep the muscles working at least a little.

The little bird seemed comfortable and curious, was interested in his surroundings, made appropriate vocalizations, and even gained weight, but for many weeks he showed no improvement in his ability to balance. Finally, after almost three months, I set him on a table and he remained upright for several seconds before toppling. Over the following days, he was able to balance for longer periods, and one day he tried to hop. Now that he finally had a little muscular control, he became restless in the sling and seemed frustrated when I put him in the padded bucket, where he was unable to see what was going on around him. So I lined a ten-gallon aquarium with cloth diapers and paper towels and brought him into our busy family room, since jays and their relatives are very intelligent and don’t thrive without mental stimulation. He seemed so delighted to be in the aquarium that I let him sleep there that night. In the morning, I was devastated to find him dead. He’d apparently wedged himself between the glass and the diaper I’d lined it with. One shoulder, on the side where he’d fallen so many times, was poorly feathered, and the bare patches of skin against the cool glass had caused him to die of hypothermia in his sleep.

Baby Blue Jay

The prognosis for birds who’ve been poisoned by lawn pesticides is bleak, and it’s also extremely difficult and often prohibitively expensive to test them to verify the cause of their illness. Many pesticide applications include a combination of different herbicides and insecticides (and sometimes fungicides), and most lawn care companies won’t divulge the ingredients in their applications (trade secrets), so it’s almost impossible to determine which pesticides killed a backyard bird or even whether pesticides were involved. There isn’t enough tissue in a small bird to get a good sample, especially if the bird didn’t actually ingest the toxin but just got some on its feathers and skin or breathed fumes. It is unconscionable to set out birdseed in yards that are treated with these dangerous chemicals.

When you purchase corn, make sure that it is intended for feeding, not planting, and never buy corn or other seed that is coated with a pink or red dye. That colored coating is capstan, a fungicide used on seeds meant for planting. It can kill mammals as large as horses and is very toxic to birds.

From 101 Ways to Help Birds, published by Stackpole in 2006. Please consider buying the book to show that there is a market for bird conservation books. (Photos, links, and updated information at the end of some entries are not from the book.)