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We have bird feeders of all shapes, sizes, and types of material. Some we've had for years. We dump out leftover bird seed and shells when we refill them. If there are obvious dangers, like algae, mold, feces or feathers, we scrape those off. We spray them with a hose, but we've never taken them down and given them thorough cleanings with soap or anything else.

We recently met someone who puts her metal, mesh and plastic feeders in the dishwasher with dishwasher detergent. The other types, like wood, she washes with soap and water, sometimes a very small amount of bleach. It's her opinion that this lowers the risk of disease to the backyard birds and the other animals who eat from those feeders.

Are our birds (examples include blue jays, grackles, starlings, sparrows, swallows, thrushes, woodpeckers, American robins, crows, cardinals, mourning doves, orioles, and others) at risk from eating out of communal feeders which haven't been cleaned? If so, what diseases are most common, so we can watch out for symptoms?

Dirty bird feeders are known for causing problems for birds,

CPW said the disease has not yet been confirmed in Colorado, but the agency wants to warn people that house finch eye disease, along with several others are commonly spread at dirty bird feeders and baths. The other diseases include salmonellosis, trichomoniasis, avian pox, pigeon paramyxovirus, and aspergillosis.

CPW warns dirty bird feeders can lead to disease

The four diseases that most frequently affect birds that use feeders are: salmonella, trichomoniasis, aspergillosis, and avian pox. All of these diseases are transmitted from one bird to another at feeding stations, especially when overcrowding occurs.

Common Bird Parasites & Diseases

The study found that while there are multiple benefits of additional food resources for wild birds, particularly during the harsher winter months, garden feeding can also promote the transmission of some diseases – not least by encouraging birds to repeatedly congregate in the same location, often bringing them into regular contact with other species they wouldn’t otherwise interact with so closely in the wider environment. Risks can be increased if hygiene at feeding stations is poor, allowing stale food, food waste and droppings to accumulate.

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Commenting further, co-author Kate Risely from BTO said: “We’re calling on everyone who feeds wild birds to be aware of their responsibilities for preventing disease. Simple steps we’d recommend include offering a variety of food from accredited sources; feeding in moderation, so that feeders are typically emptied every 1-2 days; the regular cleaning of bird feeders; and rotation of feeding sites to avoid accumulation of waste food or bird droppings."

Feed the birds? Scientists highlight risks of disease at garden bird feeders

It looks like dirty bird feeders are a problem, and overcrowding can be a problem too, but so long as they are cleaned regularly, the positives outweigh the negatives for the birds.