Greenfinch Disease Welfare: Trichomonosis and Garden Bird Health

Greenfinches have suffered severe population declines due to trichomonosis, a parasitic disease spread at garden feeders. Feeder hygiene is a direct welfare action every garden bird feeder can take.

Key Facts

UK greenfinch populations fell by around 35% between 2004 and 2016 largely due to trichomonosis
Trichomonosis is caused by the protozoan parasite Trichomonas gallinae, spread through contaminated food
Infected birds develop yellow lesions in the throat, preventing swallowing - causing a slow death by starvation
Garden feeders concentrate birds and create disease transmission hotspots
The disease also affects chaffinches and is expanding into other seed-eating species
Regular feeder cleaning with appropriate disinfectant can significantly reduce transmission

Welfare Considerations

Greenfinch trichomonosis represents one of the clearest cases where human-provided feeding, intended to help wildlife, has inadvertently caused welfare harm at population scale. Millions of garden bird feeders became disease transmission hubs from the early 2000s. The suffering of affected individual birds - unable to swallow, progressively weakening over days - is severe. Simple hygiene measures can substantially reduce this welfare harm. The BTO's Garden Wildlife Health project provides free guidance on best feeder hygiene practice.

What You Can Do

Clean all garden bird feeders at least weekly with a 5% disinfectant solution
Remove any sick or lethargic greenfinches from feeder areas to prevent disease spread
Report sick or dead birds at feeders to Garden Wildlife Health (gardenbiodiversity.org)
Use multiple small feeders spread apart rather than one large congregating feeder
Support BTO research into avian disease through the Garden Wildlife Health scheme