For millions of cold and hungry birds, feeders hanging in gardens are a lifeline during the hard days of winter.  But some wildlife experts are warning that they can also be a deathtrap. Dirty feeders and infected bird baths are spreading a disease that has killed a fifth of Britain's greenfinches in recent years.

In Britain, around one in five greenfinches has been killed by the disease Trichomoniasis since 2005. In 2007, around 500,000 greenfinches were killed by Trichomoniasis according to the British Trust for Ornithology. Other types of finches, pigeons and house sparrows are also susceptible.

The Royal Society for the Protection of Birds says feeders saved the lives of countless birds but bird tables should be cleared of food and scrubbed with weak bleach and water once a fortnight. Water containers should be washed out, and feeders should be washed.