Outbreaks of disease may occur in populations of wild birds wherever they occur, including those visiting gardens. Because garden birdwatchers take so much interest in the birds visiting their gardens, they may occasionally come across diseased birds and a number of different diseases have been reported from birds seen at garden feeding stations. These include those caused by Salmonella and E. coli but other, less familiar disease may also occur.

It is known that the transmission of disease between individuals tends to be increased where birds gather together in large numbers and this may go some way to explaining why some species may be more susceptible than others.

Anecdotal evidence suggests that some bird species may be more susceptible to disease than others. Certainly, Greenfinches, Chaffinches, Siskins, House Sparrows and Collared Doves appear to be the most commonly reported victims of diseases. This may, in part, reflect the gregarious nature of these birds and their tendency to feed in flocks.