Researchers Warn Bird Feeders Could be Aiding the Spread of Disease

Rare diseases among bird populations are on the rise, and scientists say that garden bird feeders are contributing to the epidemic levels currently being seen in some species.

Researchers from the Zoological Society of London and the British Trust for Ornithology have discovered a couple of factors that are lending themselves to the spread of diseases, both linked to the use of bird feeders. One of these is the state of bird feeders themselves which many people do not think to clean, leaving stale food to rot and bird droppings to accumulate. The other is that bird feeders provide a meeting point for species of bird that would never usually interact and this is the main driver behind the spread of diseases.

Finch Trichomonosis is one disease which has seen an increase thanks in part to bird feeders. The disease first emerged in finches in 2005, and since then has decreased the Greenfinch population by 35%. Trichomonosis causes lesions in the throat of the bird making it hard for it to swallow. Eventually eating becomes difficult and the bird finds itself unable to swallow and spits food out or vomits it out. This can cause serious consequences at bird feeders where the contaminated food is then available for other birds to eat, thus passing on the disease. It can also be passed on through regurgitation from one bird to another. Other symptoms include fluffed up plumage, lethargy and difficulty breathing. It is most common in pigeons, doves and finches, first appearing among finches in 2005.

By Derek Keats from South Africa (Coke bottle feeder) [CC BY-SA 2.0 (], via Wikimedia Commons

By Derek Keats from South Africa (Coke bottle feeder) [CC BY-SA 2.0 (], via Wikimedia Commons

The data was collected using a combination of the RSPB’s Big Garden Bird Watch scheme which invites members of the public to to contribute observations, and a large scale surveillance project carried out by the British Trust for Ornithology (BTO), Zoology Society of London and Fera Science Ltd which has spanned the past 25 years. There were three main types of disease this surveillance project aimed to study; protozol parasite (which causes Trichomonosis), bacterial (Passerine Salmonellosis) and viral (Paridae Pox). As well as the increase in the levels of Trichomonosis among finches a rise in Paridae Pox,, also a disease which has recently emerged, was also discovered. Passerine Salmonellosis on the other hand, previously a common disease, was found to have reduced to a low level.

Kate Risely from the BTO offers this advice to anyone who wishes to keep bird feeders:

“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 one to two days; the regular cleaning of bird feeders; and rotation of feeding sites to avoid accumulation of waste food or bird droppings.”

If you notice birds showing symptoms of Trichomonosis or other disease in your garden then the RSPB recommends to temporarily stop putting food out until no further sick birds are found in the garden as a way to help slow and stop the outbreak.

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Jessica Howard

Jessica Howard

31 years old, currently living and working in London, UK.

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