We’ve been seeing some reports on TN birding sites of House Finches and Goldfinches with an eye disease known as Mycoplasmal conjunctivitis, or House Finch eye disease. And just yesterday a customer inquired about a bird that seemed sick. It did not move away as she approached, as if it was not really aware of her presence. The bird turned out to be a sick House Finch. We hear reports and see evidence of this every year that range from sparse to wide-spread.
Birds infected with House Finch eye disease have red, swollen, runny, or crusty eyes. In extreme cases the eyes become swollen shut and the bird becomes blind. House Finch eye disease is caused by the bacterium Mycoplasma gallisepticum. This bacterium has long been known as a pathogen of domestic turkeys and chickens, but it has been observed in House Finches since 1994. The disease has affected several other species, including American Goldfinch, Evening Grosbeak, and Purple Finch
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 House Finch eye disease has affected mainly the eastern House Finch population, which is largely separated from the western House Finch population by the Rocky Mountains. 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. In 2006, however, the disease was found west of the Rocky Mountains, and researchers are using FeederWatch data to monitor the spread west.
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.
According to the Cornell Lab of Ornithology, House Finch Disease Survey data tell us that the disease has decreased from epidemic proportions and is now restricted to a smaller percentage of the population. It’s estimated that 5% to 10% of the eastern House Finch population has this disease and that the dramatic spread that occurred a few years ago has subsided. This means that it is still an important and harmful disease, but that House Finch populations are not currently at extreme risk of wide-spread population declines.
What To Do
If you detect a sick finch at your feeders the standard procedure is to take down your feeders for a few days to a week and give them a very thorough cleaning. Cleaning your feeders is always a good idea and is recommended it be done on a regular basis. Clorox wipes are very handy to give your feeder a quick clean particularly around the feeding ports.