BTO Parasite threatens Britain's garden birds


Scientists from the Garden Bird Health initiative (GBHi) have discovered that trichomonosis, an emerging infectious disease of garden birds, led to dramatic declines in Greenfinch populations across much of England. In central England the population declined by a third within a year of the emergence of the disease. The study also revealed that Chaffinch populations fell by up to 20%. 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.

The Trichomonas gallinae parasite responsible for the declines. (Photo: GBHi)

Trichomonas gallinae, the cause of the disease, is a protozoan parasite (not a virus). It is well known as a cause of disease in pigeons and doves, and also the birds of prey that feed on them. In 2005, trichomonosis was first recognised as a cause of disease in British finches, with Greenfinch and Chaffinch most affected, although a range of garden birds have been found to be susceptible to the parasite. Trichomonas is vulnerable to desiccation and cannot survive for long periods outside the host. Transmission is most likely to be through birds feeding one another with regurgitated food during the breeding season; or through food or drinking water contaminated with saliva. A disease fact sheet on trichomonosis is available on the GBHi website.

Outbreaks are most severe and frequent in the period August to October and sick birds are obvious, as they have a tendency to stay close to feeders and water sources, and often die there. Lack of birds in the garden without the presence of sick or dead birds does not indicate a disease outbreak, but is most likely caused by the seasonal changes in birds' behaviour in late summer and autumn.

Dr Rob Robinson, a Principal Ecologist at the BTO, commented: "These findings demonstrate that virulent infectious diseases can cause sharp population declines in common wild birds in just a short period of time."

In order to determine the scale of the disease outbreak, the study drew data from observations from members of public and a volunteer survey. Further data were collected through post mortem examination of hundreds of birds collected from gardens across the country.

Greenfinch, Summer Leys LNR, Northamptonshire (Photo: Mark Digby)

Becki Lawson, a wildlife veterinarian at the Zoological Society of London, 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 on Greenfinch and Chaffinch populations 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 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 help the project by reporting cases of disease or mortality in their garden birds online.

The GBHi was established in 2003 to develop and publish guidelines about how best to feed garden birds to maximise the benefits for their conservation and welfare and to undertake a major garden bird health surveillance and research project. The surveillance and research project is a joint initiative of the BTO, Zoological Society of London, RSPB, Universities Federation for Animal Welfare, Scottish Agricultural College, University of Liverpool, and the Wildlife Veterinary Investigation Centre, with other collaborating organisations. The GBHi uses volunteers to record disease incidents from the general public and the BTO Garden BirdWatch scheme, enabling scientists to track the impacts of this emerging disease on garden bird populations.

Related pages

Chaffinch Chaffinch
Greenfinch Greenfinch

Related articles

BTO Calling all young birders! BTO Calling all young birders!
Spurn Bird Observatory, Next Generation Birders and the British Trust for Ornithology are once again running a competition to find the Martin Garner Spurn Young Birder of The Year. read on read on
BTO Citizen scientists needed BTO Citizen scientists needed
The BTO is asking for volunteers to monitor nests as part of its House Martin Survey. read on read on
BTO Thrushes prosper in British gardens BTO Thrushes prosper in British gardens
Blackbirds, Song Thrushes and Mistle Thrushes were all recorded in good numbers during BTO's Garden BirdWatch in 2016, but some species fared poorly. read on read on
BTO Help complete the most ambitious bird atlas ever produced BTO Help complete the most ambitious bird atlas ever produced
The British Trust for Ornithology (BTO) has just launched a new web-based tool for filling British and Irish gaps on the map for the new European Breeding Bird Atlas (EBBA2), the most ambitious continental-scale atlas of breeding birds ever produced. read on read on
BTO You never know what's in store with the Breeding Bird Survey ... BTO You never know what's in store with the Breeding Bird Survey ...
Sarah Harris outlines why it's important for you to help out with the annual Breeding Bird Survey (BBS). read on read on

The information in this article was believed correct at the time of writing. BirdGuides accepts no responsibility for errors, or for any consequences of acting on information in the article. The opinions expressed are those of the author(s) and are not necessarily shared by BirdGuides Ltd.

hide section Reader comments (1)

I live in west Wales near the entrance to Ynys Hir RSPB reserve and have experienced this desease amongst the feeding garden birds for three years, I understand that the RSPB have also experienced some problems. Initially it only seemed to affect the greenfinches but soon included chaffinches as mentioned in the article. However, last winter at least seven Siskin were also found dead in the garden all appeared to have died from Tricomonas. I regularly clean the feeders and the ground...more more
   Mervyn Lloyd, 26/08/10 12:18Report inappropriate post Report 

Back to top Back to top

Latest edition Latest edition
Search articles Search articles
All articles All articles
Popular articles Popular articles
Privacy Policy | Terms of Use | Terms of Sale | Cookie Policy | About us | Advertise | Contact us
BirdGuides, Warners Group Publications PLC, The Chocolate Factory, 5 Clarendon Road, London N22 6XJ
© 2017 BirdGuides and Warners Group Publications plc. All Rights Reserved. Company Registered in England no. 2572212 | VAT registration No. GB 638 3492 15
Sales: or tel. 0800 919391 · International Sales: +44 (0)1778 391180 · Office: or tel. 020 8826 0934

Fatbirder's Top 1000 Birding Websites