While many people enjoy feeding birds, improperly maintained feeders can put birds at risk. Birdfeeders and bird baths can serve as reservoirs for several diseases found in birds including salmonellosis, trichomoniasis, aspergillosis, avian pox, and conjunctivitis. If sick birds are noticed at feeders, stop feeding the birds, clean the feeders with a dilute (10 percent; one cup bleach to nine cups water) bleach solution, and wait three to four weeks before feeding the birds again. Properly maintained feeders can help reduce the spread of these diseases.
For more information about bird feeder maintenance, read the Audubon Society's guide to feeder maintenance and hygiene.
An even better way to attract birds to your yard is to plant a mix of trees, shrubs, and flowers that provide natural food sources, cover, and nesting sites for birds. Providing natural sources of food rather than stocking bird feeders will reduce the concentration of birds in one area, thereby reducing the likelihood of healthy birds coming into close contact with sick birds.
For more information about diseases at birdfeeders, read the National Wildlife Health Center's fact sheet on coping with diseases at bird feeders.