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Help us learn more about House Finch eye disease! Join Now!
Birds infected with House Finch eye disease (also called Mycoplasmal conjunctivitis) have red, swollen, runny, or crusty eyes. In extreme cases the eyes become swollen shut and the bird becomes blind. You might observe an infected bird sitting quietly in your yard, clumsily scratching an eye against its foot or a perch. While some infected birds recover, many die from starvation, exposure, or predation. The disease has affected several other wild bird species, including American Goldfinch, Evening Grosbeak, and Purple Finch.
Will the disease impact these species as much as it impacted House Finch populations? At what rate will the epidemic spread among these species? Data from Project FeederWatch participants will help us find out.
In the winter of 1994, Project FeederWatch participants in the Washington, D.C., area began reporting that House Finches at their feeders had swollen, red, crusty eyes. Lab tests revealed that the birds had Mycoplasma gallisepticum, a parasitic bacterium previously known to infect poultry. Mycoplasmal conjunctivitis, as the disease is sometimes called, spread rapidly across the Eastern Seaboard, leaving House Finches listless, mostly blind, and vulnerable to predators and bad weather.
Until the 1940s, House Finches were found only in western North America. They were released to the wild in the East after pet stores stopped illegal sales of “Hollywood Finches,” as they were commonly known to the pet bird trade. The released birds successfully bred and spread rapidly throughout eastern North America.
Initially, House Finch eye disease primarily affected the eastern House Finch population, which is largely separated from the western House Finch population by the Rocky Mountains. In 2006, however, the disease was found west of the Rocky Mountains and has since spread to House Finch populations throughout the west.
Starting in 1994, because of the efforts of participants across North America, the Cornell Lab of Ornithology started the House Finch Disease Survey. This survey collected data on the spread and prevalence of a bacterial disease that now affects House Finches from the Atlantic to Pacific coasts. These data have been invaluable for documenting the spread of the disease and have motivating research that seeks to understand the reasons for persistence of the disease as well as its longer-term impact on House Finch abundance.
In 2008, the House Finch Disease Survey ended as a stand-alone project, but monitoring the disease continued through the data collection protocol in Project FeederWatch. We encourage FeederWatchers to look for signs of the disease in House Finches, American Goldfinches, and a few other finches coming to their feeders and to report whether they see it or not. Importantly, looking for the disease and NOT seeing signs of it is as valuable to report as observations of disease presence. Learn more on the FeederWatch blog.
Birds with avian conjunctivitis often have red, swollen, watery, or crusty eyes; in extreme cases the eyes are so swollen or crusted over that the birds are virtually blind.
Avian pox is another disease that affects House Finches. This disease is characterized by wart-like growths on the featherless areas of the body such as around the eye, the base of the beak, and on the legs and feet. Avian pox can be mistaken for conjunctivitis when the eyes are affected. “Growths” on the eye are typically from avian pox.
Photo by Chris Bumbar Photo by Chris Bumbar
Learn what researchers discovered about disease transmission from eye disease research on the All About Birds Blog.
In 2018, researchers studying the disease found that the pathogen that causes House Finch eye disease, Mycoplasma gallisepticum, is becoming stronger and more dangerous than earlier versions of the pathogen. Learn more on the FeederWatch blog.
Learn how to distinguish House Finches from the similar Purple Finch and Cassin’s Finch on our Tricky Bird ID page.
Learn more about House Finch biology on the All About Birds page.
Because it is especially important to know where eye disease is absent as well as where it is present, we are only able to take reports of sick birds from registered FeederWatch participants, who report observations of eye disease along with their regular counts. Learn more about Project FeederWatch in the About section of this website.
Infected birds have red, swollen, runny, or crusty eyes; in extreme cases the eyes become swollen shut or crusted over, and the birds become essentially blind. Birds in this condition obviously have trouble feeding. You might see them staying on the ground, under the feeder, trying to find seeds. If the infected bird dies, it is usually not from the conjunctivitis itself, but rather from starvation, exposure, or predation as a result of not being able to see.
Avian pox is another common disease that affects a bird’s eyes. This disease causes warty lesions on the head, legs, and feet but cannot always be easily distinguished from conjunctivitis. Avian pox is transmitted by biting insects, by direct contact with infected birds or contaminated surfaces (e.g. feeders), or by ingestion of contaminated food or water. Just as with conjunctivitis, the infected bird becomes vulnerable to predation, starvation, or exposure.
Although infected birds have swollen eyes, the disease is primarily a respiratory infection. It is caused by a unique strain of the bacterium, Mycoplasma gallisepticum, which is a common pathogen in domestic turkeys and chickens. The infection poses no known health threat to humans and had not been reported in songbirds prior to this outbreak. Researchers at various institutions are currently trying to learn more about the transmission, genetics, and development of this disease.
Conjunctivitis was first noticed in House Finches during the winter of 1993-94 in Virginia and Maryland. The disease later spread to states along the East Coast and has now been reported throughout most of eastern North America, as far north as Quebec, Canada, as far south as Florida, and as far west as California.
So far, the disease is most prominent in House Finches and somewhat prevalent in American Goldfinches. However, reports of the disease have been confirmed in Purple Finches, Evening Grosbeaks, and Pine Grosbeaks, all members of the family Fringillidae.
House Finches are not native to eastern North America. Until the 1940s, House Finches were found only in western North America. Some birds were released to the wild in the East after pet stores stopped illegal sales of “Hollywood Finches,” as they were commonly known to the pet bird trade. The released birds successfully bred in the wild and spread rapidly throughout eastern North America. Because today’s eastern House Finch populations originated entirely from a small number of released birds, they are highly inbred, exhibit low genetic diversity and, may therefore be more susceptible to disease than other bird species native to the East.
The House Finch population is large, and the birds tend to move together in highly mobile foraging flocks. Therefore, diseased individuals are constantly entering new areas, increasing the chance of infecting other birds in that area. Also, some infected birds do not die from the disease, which increases the probability of its transmission to other individuals. Lastly, current evidence suggests that infected birds do not acquire immunity to future infections.
Whenever birds are concentrated in a small area, the risk of a disease spreading within that population increases. Research suggests that House Finches that spend large amounts of time at feeders spread the disease more effectively. Read more about the research linking feeder behavior to the acquisition and transmission of eye disease on our blog. Nevertheless, the disease has decreased from epidemic proportions and is now restricted to a smaller percentage of the population. We estimate that 5% to 10% of the eastern House Finch population has this disease and House Finch populations are not currently at extreme risk of wide-spread population declines. Even so, please be responsible and clean your feeders on a regular basis even when there are no signs of disease.
We encourage people to take down their feeders for at least a few days to encourage sick birds to disperse. While the feeders are down, clean them thoroughly. You can use a dishwasher on a hot setting, or wash them with soap and boiling water, a diluted bleach solution, or a weak vinegar solution (10%). Be sure to remove any build-ups of dirt around the food openings. Rinse the feeders thoroughly and let them dry completely before rehanging them. Also rake underneath the feeders to remove old seed and bird droppings. Be sure to continue to clean your feeders every week or so. If sick birds return, avoid using feeders with big ports that the birds can rub their heads against.
By law, only licensed professionals are authorized to handle most wild birds. Although it is possible to treat finches with conjunctivitis, you should not add medications to bird seed or baths under any circumstances. There is no way to know if medication actually helps birds in uncontrolled conditions, and such treatment may in fact contribute to disease spread by allowing infected birds to survive longer. Treatment with antibiotics may also lead to the rapid evolution of novel strains of the disease that could possibly spread to other songbirds.