Because feeders offer you an up-close view of birds, and because birds seek out easy meals when their health is compromised, you might occasionally see a sick bird at your feeder. Only veterinarians or federally licensed wildlife rehabilitators can legally treat wild birds. If you see a bird that appears to be compromised in some way, perhaps due to sickness or injury, do not try to care for the bird yourself. It is illegal for you to possess most wild birds unless you are under the direction of someone licensed for their care.
If a sick bird comes to your feeder, minimize the risk of infecting other birds by cleaning your feeder area thoroughly. If you see several sick birds, take down all your feeders for at least a week to give the birds a chance to disperse. Remember that prevention is the key to avoiding the spread of disease. Regularly clean your feeders even when there are no signs of disease.
Birds infected with House Finch eye disease (also called Mycoplasmal conjunctivitis) 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. Learn more about House Finch eye disease.
Two forms of avian pox exist. In the more common form, wart-like growths appear on the featherless areas of the body, such as around the eye, the base of the bill, and on the legs and feet. In the second form, plaques develop on the mucous membrane of the mouth, throat, trachea, and lungs, resulting in impaired breathing and difficulty feeding.
Avian pox can be caused by several strains of the pox virus and has been reported in at least 60 species of birds, including turkeys, hawks, owls, and sparrows. The virus can be spread by direct contact with infected birds or contaminated surfaces (e.g., feeders) or by ingestion of contaminated food or water.
Salmonellosis is caused by bacteria belonging to the genus Salmonella. It is a common cause of mortality in feeder birds, but the symptoms are not always obvious. Sick birds may appear thin or fat and fluffed up and may have swollen eyelids. They are often lethargic and easy to approach. Some infected birds may show no outward symptoms but are carriers of the disease and can spread the infection to other birds.
Salmonellosis is primarily transmitted by fecal contamination of food and water by sick birds, though it also can be transmitted by bird-to-bird contact. Occasionally, outbreaks of the disease cause significant mortality in certain species including Pine Siskin, Common Redpoll, and American Goldfinch.