Greenfinch Trichomonosis and Garden Feeder Disease

The greenfinch has suffered one of the most dramatic disease-driven declines of any British garden bird, with trichomonosis spread through contaminated garden feeders having killed an estimated 35% of the UK population since 2005.

Key Facts

UK greenfinch numbers declined by around 35% between 2005 and 2016 due to trichomonosis
The disease causes a lesion in the throat that prevents swallowing, leading to starvation
Trichomonosis is spread through regurgitated food contaminated with the parasite Trichomonas gallinae
Garden feeders concentrate birds and facilitate transmission through contact with contaminated food and water
The disease has also affected chaffinches and other seed-eating birds, though greenfinches are most severely affected

Welfare Considerations

Greenfinch welfare at garden feeders is severely compromised by trichomonosis transmission that causes a prolonged, distressing death through starvation as the throat lesion grows. Infected birds become progressively lethargic, fluffed up, and unable to swallow. The primary welfare intervention is feeder hygiene, which can dramatically reduce transmission rates. Removing feeders temporarily when sick birds are present allows the local population to disperse and reduces epidemic transmission.

What You Can Do

Clean all bird feeders and water dishes weekly with a weak disinfectant solution and allow to dry fully
Remove feeders immediately if you see lethargic, fluffed greenfinches and report to Garden Wildlife Health
Use multiple smaller feeders rather than one large feeder to reduce bird contact density
Provide fresh food only; remove stale food promptly to prevent mould and bacterial growth
Report greenfinch sickness to the BTO and RSPCA Garden Wildlife Health project for disease surveillance