Garden birds under threat as deadly parasite disease jumps species barrier

Third of the greenfinch population wiped out

August 2010: Greenfinch populations in Central England dropped by a third within a year of the emergence of a new disease, reports a newly published study. Scientists from the Garden Bird Health initiative (GBHi) discovered that trichomonosis, an emerging infectious disease of garden birds led to dramatic declines in greenfinch populations across much of England.

DRAMATIC DECLINE: The greenfinch. Picture: Kay Packenham

The study also revealed that chaffinch populations fell by up to a fifth. Most birds died in the summer and autumn months, and outbreaks of the disease have continued to occur each year since its emergence in 2005.

Dr Rob Robinson, a principal ecologist at the British Trust for Ornithology (BTO) and joint lead author of the study, said: ‘These findings demonstrate that virulent infectious diseases can cause sharp population declines in common wild birds in just a short period of time.'

Invaluable help from members of public
In order to determine the scale of the disease outbreak, the study used data drawn from public observation and a volunteer survey. Further data were collected through post-mortem examination of hundreds of birds, collected from gardens across the country. Becki Lawson, a wildlife vet at the Zoological Society of London and joint lead author, said: ‘This citizen science project highlights the valuable role that volunteers can play in helping us learn more about wildlife diseases, even by just watching birds in their gardens for a couple of hours each week.'

Trichomonosis is well known in doves and pigeons but appears to have jumped the species barrier in 2005. The current effects of the disease in greenfinches and chaffinches highlight the highly unpredictable impact of parasites able to move between different species.

James Kirkwood, chief executive of the Universities Federation for Animal Welfare and founder of the Garden Bird Health initiative said: ‘Health surveillance of British wildlife species is crucial for us to recognise new and emerging disease threats that not only adversely affect the welfare of individual animals, but have the potential to impact entire populations.'

The GBHi team is now investigating possible factors underlying the emergence of this disease in garden birds and its continued impact on our garden birds. Members of the public can assist this ongoing project by reporting cases of disease or mortality in their garden birds -