Gardeners in the UK spend around £200 million a year on bird food, which helps some of Britain’s most beloved species get by in the harsh winter months and beyond.
But research by Zoological Society of London (ZSL) and the British Trust for Ornithology (BTO), suggests that bird tables and feeders are spreading illness because they bring species together which would never normally come into contact.
The risk of disease is also increased if bird tables and other feeding stations are not kept clean, so stale food, food waste and droppings accumulate, the report warned.
The study, used information on birds visiting gardens and observations of disease from citizen science project, the BTO's Garden BirdWatch scheme which sees volunteers submitting findings year-round.
It combined information from the large-scale surveillance scheme over 25 years with post-mortem examinations of birds, to track some of the most common diseases.
They found that the diseases spread rapidly through populations which were frequently meeting at feeders and bird tables.
Finch trichomonosis, for example, emerged in British finches in 2005 but soon spread to gregarious seed-eating species that visit garden feeding stations, the research showed.
Co-author Kate Risely from BTO said: "We're calling on everyone who feeds wild birds to be aware of their responsibility 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."
British gardens have become a haven for many birds which have suffered from habitat loss and urbanisation, and some 48 per cent of households regularly leave food out to help garden visitors.
The report also noted that there was also a well-being aspect to feeding the birds which helps the growing disconnect from nature and fosters interest in wildlife and conservation.
However the report points out that there a risks from feeding the birds, including that they will become reliant on the food and stop being able to fend for themselves.
“There is a need to balance the risks and benefits of supplementary feeding of garden birds to both wildlife and people,” the report concludes.
When disease outbreaks do occur, people are encouraged to report their observations to the Garden Wildlife Health (GWH) project, seek veterinary guidance; and consider a temporary halt to garden feeding in order to encourage birds to disperse, reducing the risk of further disease spread.
The researchers also hope that long term information about three of Britain’s deadliest bird diseases will help contain the spread of illness.
Commenting on the study, lead author Dr Becki Lawson from ZSL’s Institute of Zoology said: “These conditions have different means of transmission – so deepening our understanding of disease dynamics will help us develop best practice advice to ensure that feeding garden birds also helps to safeguard their health”.
The research was published in the journal Philosophical Transactions of the Royal Society B.