This winter/spring we have witnessed a handfull of goldfinches and house finches acting oddly at the bird feeders. These birds would fly from feeder to feeder more like they were lost than with the usual confidence one would expect from a bird. These same birds were often the last to respond, or didn't respond at all, when other birds quickly flee from the feeding station. Sometimes they'd shake their heads in fits or could be found sitting motionless on the ground, looking lost, amoungst a hungry group of sparrows and juncos. With a good look through the binoculars, we could see these birds were not healthy.
These birds were exhibiting the telltale behaviors of a bird with Mycoplasmal conjunctivitis. Conjunctivitis, as it is usually referred to, is a respiratory disease caused by the M.conjunctivitis bacterium. The physical symptoms of the disease include crusty, swollen tissue around one or both eyes, or thoroughly red, swollen, and oozing eyes in severly infected individuals, resulting in virtual blindness.
Goldfinch showing symptoms of conjunctivitis at my feeder
The same goldfinch trying to see from the swollen eye
The goldfinch in the photos above was seen for two days at the cottage feeders. That was Day 1, when he could still open the left eye and barely see from the right eye. The next day I saw, presumably, the same goldfinch with more advanced symptoms sitting on the ground trying the scavenge any seeds it could manage to find. I didn't see it after the third day.
Conjunctivitis is most common, and was first reported, in House Finches. The first reports of this disease came from the Washington, D.C. area in the winter of 1993-1994. From there it has spread all the way up and down the eastern US and Canada. Obviously goldfinches are susceptible to the disease in addition to Purple Finch, Evening Grosbeak, and Pine Grosbeak.
There is still a lot of mystery about the disease, including how finches have contracted it without other species showing no signs of infection, how it is spread, and how much of an impact this type of infection has on those species' populations that are affected.
Common sense and general rules to prevent the spread of avian disease apply when birds with conjunctivitis are noticed at a feeder or feeding station:
If diseased birds are observed at the feeders, take them down and wash with a 10% bleach solution. Spread feeders out to reduce crowding. Rake the area under the feeders to remove moldy seeds and bird droppings. You may want to remove all feeders for a day or two to break up a high concentration of feeding birds while ill birds are in the area. Most birds with the physical symptoms are unlikely to return to the feeding station after a day or two, due to the fact that they're likely to pass from starvation, over-exposure to environmental conditions (cold, snow, heat, rain, etc), or predation due to their loss of vision.
We have recently removed all of the seed feeders from the museum feeding station and at the naturalist's cottage. Having done so has resulted in the dispersal of the numerous house finch and goldfinch flocks from the feeding stations. The birds are still around and quite capable of locating other food sources. We are expecting to place the feeders back out later this week now that most of the birds have dispersed.
The technical information for this blog was taken from the House Finch Disease Survey, a project of the Cornell Lab of Ornithology. Visit their website for more information about conjunctivitis and learn how you can participate in the survey.
Adam Zorn - Naturalist