Disease Among Backyard Birds
What diseases occur among backyard songbirds?
There are two primary diseases that we see in our area. The first is conjunctivitis, also known as house finch eye disease, which is most common among House Finches and usually appears as swollen or crusty areas primarily around the eyes. This occurs sporadically among House Finches at all times of year, and can infrequently appear among other finch species. The less common avian pox has similar symptoms, affects the same birds, and should be responded to in the same way.
The second is salmonellosis, caused by salmonella bacteria. This disease is almost exclusively seen in winters when we have large numbers of Pine Siskins, a northern finch species that travels south in large numbers in so called “irruption years” of varying magnitude every few years. The symptoms of salmonellosis are puffed up feathers and extremely lethargic behavior—if the bird appears to be closing its eyes and does not respond to stimuli but remains perched when other birds flee, it is likely sick. It is overwhelmingly seen among Pine Siskins, but can spread to goldfinches and infrequently to other birds. This is the only common songbird disease that is communicable to pets and humans, so if you are seeing siskins with these symptoms make sure to keep cats and other pets away from birds and to wash your hands thoroughly after handling your feeders.
What should I do if I see a sick bird?
Cornell Lab of Ornithology on “if you see one or two diseased birds” (as is more common with conjunctivitis or avian pox): “Take down your feeders and clean them with a 10% bleach solution (1 part bleach and 9 parts water). Let them dry completely and then re-hang them.”
Cornell Lab of Ornithology on “several sick birds” (as in a salmonellosis outbreak): “Take down all your feeders for at least a week to give the birds a chance to disperse.” (And clean feeders, ideally with a 10% bleach solution.)
Salmonellosis is mostly seen among Pine Siskins during irregular winters when we have large numbers of these birds. You can continue to use feeding methods that don't attract siskins, such as hummingbird feeders, suet and nut feeders, or offering straight millet for ground-feeding birds like sparrows, doves, and quail. If you have suddenly have lots of siskins, you may want to take some precautionary measures even if you don't see any sick birds: be extra diligent in keeping feeders clean, limit the use of tray feeders (where infected droppings could contact food), and rotate feeder positions if siskins are feeding on the ground where droppings are accumulating.
Do birdfeeders spread disease?
Cornell on conjunctivitis: “...feeding birds may not necessarily increase the rate of disease spread, and should not have a net negative impact on the House Finch population.” “The disease probably spreads most rapidly where the birds sleep together in large, crowded roosts, quite often among populations that do not make regular use of bird feeders.”
Cornell on salmonella: “...there’s no way to know if disease transmission at feeders is any less or greater than disease transmission in the wild. Birds that contract and spread diseases, such as salmonellosis, at feeders are typically social by nature and would aggregate whether at feeders or not.”
The common perception of a correlation between feeders and disease sightings is explained by the pattern of observation: most close observation of House Finches and Pine Siskins occurs at feeders, and it is largely from feeding stations that birds are seen and reported to wildlife clinics.
How often and how should I clean my feeder?
Seed feeders should generally be cleaned once or twice a month, with tray feeders (where food could come in to contact with droppings) being cleaned more often. Suet feeders can generally be cleaned less often, as they generally do not attract the flocking finches which are both our most numerous and disease-prone birds. Hummingbird feeders should be cleaned and filled with fresh nectar once a week, or twice a week in hot weather. Most sources recommend a 10% bleach solution for the most thorough sanitizing; a 50% vinegar solution or commercially available enzyme-based cleaners can also be used.
Cornell: “You should clean your feeders about once every two weeks… For best results wash your feeder thoroughly in soapy water, then soak or rinse it in a solution of one part bleach to nine parts water. Dry the feeder thoroughly before refilling.
National Audubon Society: “Immerse your seed feeder or birdbath in a nine to one water-bleach solution, rinsing it thoroughly, one to two times per month.”
US Fish and Wildlife: “A thistle feeder for goldfinches should be cleaned about once a month… Sunflower and suet feeders may need to be cleaned only once a month.”
To learn more about these diseases and birdfeeding, visit the Cornell Lab of Ornithology’s Project Feederwatch. Many sources have inaccurate information about bird disease, but this website is run by the nation’s preeminent avian scientists.