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Trouble Brewing At Backyard Bird Feeders
Talking negatively about feeding birds seems almost blasphemous. But imagine this--millions of well-intentioned backyard birders could be innocently harming the creatures they love to feed. As unimaginable as that seems, researchers are coming up with more cases of bird diseases that can be traced to transmission at feeders. While it is said that birds of a feather flock together, it is also beginning to include those which may have a transmittable disease.
In a recent edition of Bird Watchers Digest (December 1999), author Eirik Blom points out that "bird feeding has become very big business. It affects billions of birds. It may have taken a while for serious controversy to emerge, but it is here, and it is serious. A lot of birds are dying because of it."
How is this happening? Researchers are finding that not only are some bird feeders encouraging the transmission of diseases just by attracting unnaturally high groupings of birds, but also, the bird feeder itself, when not taken care of correctly, can cause birds to become ill.
The problems are many. One of the most well-known and widespread diseases is mysoplasmal conjunctivitis or what has become known as house finch disease. The disease, which has spread throughout most of the species' eastern range, causes the eyes of an infected bird to become swollen and crusty. This can lead to blindness and death from starvation, as the birds become unable to forage for food. Although known as house finch disease, it has recently been discovered in goldfinches and downy woodpeckers. According to the Cornell Laboratory of Ornithology, conjunctivitis is spread when healthy birds come into contact with an infected bird or an object touched by a diseased bird. An example is the tube feeder which requires the bird to stick its head into a hole in order to extract seeds. When the eyes of an infected bird come in contact with the opening, the next bird to feed at that perch may pick up the disease.
For this reason, feeders should be cleaned with a solution of one part bleach to 10 parts water every two weeks or so. Nevertheless, 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 birdfeeders, Cornell scientist Andre Dhondt suggests.
Using data collected since 1988 by the Lab's Project Feederwatch (http://birds.cornell.edu/pfw) and the Audubon Society's over 100 year-old Christmas bird count, Dhondt was able to track the emergence of the disease and compare populations before and after its introduction. While Dhondt believes the disease has now stabilized, there has been a tremendous decrease in the number of house finches in the East from 300 to 180 million birds.
While conjunctivitis may have stabilized, the National Wildlife Health Center (NWHC) in Wisconsin is tracking two other diseases with ties to bird feeders: salmonella and avian pox. Currently, mortality due to salmonellosis has been confirmed as the cause of death in birds in all states except Connecticut and Missouri. The primary species affected are goldfinches, pine siskins and redpolls. Quite plainly, NWHC researchers explain salmonellosis is a bacterial disease and a common cause of mortality in birds at bird feeders.
Salmonella can be spread from bird to bird through direct contact or through ingestion of food or water contaminated with feces from an infected bird or mammal. Carriers of the organism may appear healthy, but shed the organism periodically in their feces. Sick birds have been observed with ruffled feathers, perching for long periods and having seizures.
To reduce the spread of bacteria, the Center suggests cleaning the feeders with a 10% bleach and water solution, and not putting the feeders back up for one to two weeks so that affected birds won't be concentrated in one location. Rake up waste seeds and droppings below the feeders. Bird feeders with rough surfaces, cracks or crevices are difficult to sanitize and should not be used. When using feeders, the location should be changed at regular intervals. Adding more feeders may reduce crowding and minimize opportunity for interaction and contamination. Finally, birdseed should be stored in rodent proof containers. A note of caution: Strains of salmonella may cause illnesses in humans, so using rubber gloves is recommended as well as cleaning all feeders outside.
The NWHC is reporting that Avian pox is infecting a variety of birds worldwide from raptors to songbirds. Caused by a pox virus, the disease is transmitted by direct contact with infected birds, ingestion of food and/or water contaminated by sick birds or carcasses, or contact with the contaminated surfaces such as bird feeders and perches.
The symptoms include wartlike growths occurring around the eyes, beak or unfeathered skin leading to difficulty seeing, breathing, feeding, or perching. Growths can also form internally in the mouth, throat, trachea and lungs resulting in difficulty breathing or swallowing. Birds with either symptom may appear weak and emaciated.
This year the WVDNR has received several reports of dead mourning doves. There deaths have been attributed to Avian trichomoniasis. This disease principally affects young birds and the infection, caused by a parasite (T. gallinae), shows up as small white to yellowish areas in the mouth cavity. Again, transmission can take place at contaminated feeders and water sources.
Different types of feeders have to be monitored carefully. During a two week period this past wet summer, twelve goldfinches were reported dead at feeders in WV. The culprit in these cases was moldy thistle bag feeders.
With all this trouble happening around the bird feeders, are researchers suggesting that feeding our feathered friends stop? Not really. Eirik Blom suggests backyard naturalists feed more wisely, and make sure everyone knows there is more to bird feeding than just filling the feeder. He suggests that flyers be handed out and that seed companies include information on their packages on the proper way to maintain feeders.
"The problem is real and is getting worse," he writes. "Millions of birds are going to die and we can do something about it."
To receive the one-page flyer The Do's and Don'ts of Bird Feeding log on to www.birdwatchersdigest.com.
Editor's Note: Some researchers feel that unnatural groupings of species at feeders may facilitate the transmission of avian diseases; providing a backyard habitat with natural food sources may be an alternative. For more information on the WILDYARDS program contact the WVDNR or if you find any diseased birds at your feeder.
Uploaded: 2/21/2004
Uploaded: 2/21/2004