Research Surprise: Many Birds Exposed to Eye Disease, but Only Finches Get Sick

By Pat Leonard
August 25, 2014
Male House Finch at feeder Male House Finch by Maria Corcacas/PFW.

“The results were shocking,” says André Dhondt, director of Bird Population Studies at the Cornell Lab of Ornithology. “More than half the bird species we tested have been exposed to the bacteria responsible for House Finch eye disease.” A paper recently published in the online scientific journal PLOS ONE shows that a bacterial parasite previously thought to infect only a few species of feeder birds actually can infect a wide range of species, though most do not show signs of illness.

New self-paced course: Learn How to Identify Bird Songs, Click to Learn More

“This organism, Mycoplasma gallisepticum, is much more widespread than anyone thought,” Dhondt explains, “although in most species there are no signs of conjunctivitis.”

Black-capped Chickadees, though exposed to the mycoplasma bacterium, do not show symptoms of eye disease. Photo by Shirley Gallant.

Species testing positive for exposure to the bacteria include feeder favorites such as Black-capped Chickadees, Tufted Titmice, and American Goldfinches. But exposure was also detected in forest species, such as the Wood Thrush.

“That was another surprise,” says Dhondt. “How on earth do Wood Thrushes get infected with mycoplasma? They’re not a feeder bird at all. Everyone has always assumed that feeders play a major role in the transmission of the disease and this study shows that’s not necessarily so.”

Dhondt’s team caught and tested nearly 2,000 individual birds from 53 species, looking for evidence of current infections (bacterial DNA) or past infections (antibodies) by Mycoplasma gallisepticum. The birds were studied in and around Ithaca, New York, between January 2007 and June 2010. The diagnostic tests revealed that 27 species of birds were infected by this bacterium. The actual number of species exposed to the bacteria could be even higher than suggested by this study because the test for antibodies is known to produce false negatives.

House Finch eye disease first appeared in North America in 1994 when people watching backyard feeders started seeing birds with swollen, runny eyes. Dhondt says that a strain of the bacteria, usually found in poultry, was able to grow successfully in House Finches (see Jumping the Species Barrier). The House Finch lineage of the bacteria has been mutating since it was first detected.

“The organism could mutate into a form that is much more virulent among other bird species and create a new epidemic,” noted Dhondt, who added that while we know that many species of songbirds are exposed to Mycoplasma gallisepticum, we still do not know whether the bacteria in other species of songbirds are identical to that living in House Finches in the same area.

This male House Finch shows obvious signs of eye disease. Photo by Errol Taskin.

While many species of songbirds can be infected by this bacterium, only House Finches regularly exhibit swollen eyes as a result of infections, and citizen-science participants in the Cornell Lab’s Project FeederWatch are still tracking the occurrence of disease in these finches. The take-home message for people who feed backyard birds remains the same: keep the feeders clean. If you see sick birds, leave them alone, take down the feeders and clean them, and be sure to wash your hands thoroughly afterward.

The paper, Diverse wild bird host range of Mycoplasma gallisepticum in eastern North America, is coauthored by André Dhondt, Jonathan C. DeCoste, and Wesley M. Hochachka from the Cornell Lab of Ornithology, and David H. Ley, North Carolina State University.

The work described in this paper is part of a larger collaborative research project that has received funding from both the NSF and NIH through their Ecology and Evolution of Infectious Diseases Initiative.

For more information about House Finch Eye Disease:


  • Caroline

    About 6 years ago a finch that seemed to be blind was at my feeders. He would continue eating as I approached, only leaving when I made noise. Initially, I thought I was doing a good thing, feeding a blind bird and I wondered if I should capture him to keep him alive as winter approached. Then his bloody scabs started to peel off and I learned about this disease.

    I stopped using the bird feeders. I only watch birds at a distance now. It is upsetting to realize I was spreading this disease for a time.

  • karen neal

    omg–your data seemed to suggest bird feeders are not the “transmitter”–worrisome!!

  • karen neal

    what did I need to moderate in my comment–I love birds so much

  • Hugh

    Hi Karen – all comments are put into a queue for moderation rather than going up on the page immediately. This is to keep spam comments from getting posted automatically. As soon as we get a chance to look over the comments the “real” ones (like yours) will appear on the page. Thanks – Hugh

  • until I moved to TN, I did not have feeders. I had never seen house finches up close and had to look up what kind they were. Now I have hundreds. I have not noticed any of them that look like this, but if I do, what should I do?

  • Mary J

    What is your recommendation regarding the use of feeders? Thanks.

  • Claudia Anderson

    I have a large amount (25 or so)of House Finches at my feeders everyday. I would say that at least 5 or 6 of them have the disease. It seems to be very prevalent in them right now… at least in my area (Dallas, TX). Usually the ones that cannot see well get caught and killed by the cats in the neighborhood.

  • Ginger

    I wonder if this is due to house finches not being native to the east coast. I understand that they were brought here from California as pets in the past. If this is true, then maybe the native birds such as chickadees have had a chance to develop an immunity to the bacteria while the house finches have not had time to evolve a tolerance for it….?

  • Virginia

    I have seen house finches with this malady picking up discarded seed from my Ringneck doves’ loft. Guess what? I think my Ringnecks have it.

  • Connie Helwich

    I had a goldfinch that was sitting on my fountain and let me pick him up with this disease. I kept him overnight and was going to take him to a wildlife rescue but he died overnight. Do fountains post a risk of this disease too? I do clean it on a regular basis. I do not have feeders.

  • Karen Biddle

    over the years I have found many finches at my feeder with what we call “eye Pox”. The eye gets crusty and closes. I have caught many of them, given them injections of Baytril, and put an antibiotic eye cream on the affected eye. I kept them in a small cage with food and water. After just a few days, their eyes had totally cleared up, and I set them free. I am very familiar with treating birds of all kinds since I work for an exotic bird breeder. It’s part of my job. I just felt good to be able to help the little finches get rid of that nasty eye.

  • Hugh

    Thanks for your comment, Karen! We’ll just add a reminder here, for other readers, that handling and treating wild birds requires training and a federal permit. Wild birds are difficult to capture and care for, so please don’t try this at home unless you have the necessary training and qualifications. Thanks – Hugh

  • Lawrence

    Just to be clear: the article quoted a researcher who suggests that bird feeders are not the ONLY means of transmission; it does NOT say that bird feeders play no role in transmission. So, as the article concluded, it is still important to clean your bird feeders.

    [This comment has been migrated from an earlier post version by Cornell Lab staff.]

  • Joan Viril

    I too worryed about a little red finch that was at my feeder from Spring and I thought was born with a eye problem. He sat on my straw hat once and I felt sorry but thought nature would take care of him as a cat would get him. As Fall was comeing near and he was still comeing to my feeder I called the Nature Center at at our Zoo. I thought if he wanted so much to live he need help. They told me if I could get him they would put in eye drops and that I should clean feeder with hot water and bleach as other birds would get it. They were suprised to see me with the bird a hour later. I have hand raised Cockateals from the egg size so know birds.

    [This comment has been migrated from an earlier post version by Cornell Lab staff.]

  • jana

    I live in Illinois and in 2013 i had to pick up a robin who was standing in the middle of the road. It had its eyes crusted over with this infection. I hope this helps your study. Next time i come across this i hope to help with salt water eye solution

    [This comment has been migrated from an earlier post version by Cornell Lab staff.]

  • waitress212

    In the last month I have seen this in a cardinal and a goldfinch at my feeder. Last year it was only house finches.

Research Surprise: Many Birds Exposed to Eye Disease, but Only Finches Get Sick