Moldy birdseed and unclean bird feeders can make birds sick, the Minnesota Department of Natural Resources said.
In spring and in hot, humid weather it is common for mold to form on wet birdseed. The mold can cause a fatal avian disease called aspergillosis, which affects the birds' respiratory systems.
Carrol Henderson, supervisor of the DNR nongame wildlife program, urges people to rake or sweep up any fallen seeds and seed hulls under their feeder to prevent moldy conditions from occurring on the ground. "These seeds can also attract meadow voles, house mice or other rodents, and the growth inhibitor in sunflower hulls can cause problems with grass or flowers near the feeder," he said.
Salmonella is another disease that affects birds and is associated with unclean feeders. It is extremely important, Henderson said, to keep a bird feeder clean to minimize the threat of disease.
To clean a feeder, he suggests using a solution of two ounces of bleach with one gallon of water and scrub the entire surface, or 10 parts water to one part bleach. Always allow the cleaned feeder to dry out in the sun, as the sunlight will help kill bacteria on the feeder. Hummingbird feeders should be cleaned about every week to 10 days during the summer to keep the sugar water from producing mold.
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Keep the feed dry by using a hopper-type feeder or a fly-through feeder and always scrape out old seed that accumulates in the corners. Tray feeders with a screen bottom will allow seeds to dry out from above and below after a rain shower. "Remember not to put out too many seeds at once because if the seeds are several inches thick, they can still become moldy in the center of a feeder with a screen bottom," Henderson said.
More information on attracting and feeding birds is available in "Wild about Birds: The DNR Bird Feeding Guide" and "Landscaping for Wildlife." Both books are for sale at Minnesota's Bookstore in St. Paul. These books were made possible by the donations to the nongame wildlife fund.
