Greenfinch Welfare: Trichomonosis in UK Garden Birds 2026

Trichomonosis, caused by the parasite Trichomonas gallinae, has caused catastrophic greenfinch population declines in the UK since 2005.

Key Facts

Greenfinch populations in the UK declined by approximately 65% between 2005 and 2016 due to trichomonosis
The parasite causes soft tissue lesions in the crop and oesophagus, preventing birds from swallowing food
Affected birds appear fluffed up, lethargic, and struggle to swallow at feeding stations
The disease spreads between birds at shared feeders through saliva on food and water contamination
Chaffinches and house sparrows are also affected, though greenfinches are most severely impacted

Welfare Considerations

Trichomonosis causes significant individual welfare compromise - affected birds experience progressive inability to swallow, starvation, and distress before death. Feeding stations where birds share food and water accelerate disease transmission, creating a welfare paradox where well-intentioned feeding may contribute to disease spread. Welfare-conscious garden bird feeding that minimises transmission risk - through regular feeder cleaning, rotation between sites, and temporary cessation when sick birds are observed - substantially reduces welfare harm. Individual birds found sick with trichomonosis require veterinary assessment, as treatment is possible in early stages.

What You Can Do

Clean bird feeders weekly with a 10% disinfectant solution to reduce Trichomonas transmission
Temporarily remove feeders if sick birds are observed to reduce transmission
Report sick greenfinches and finches to the Garden Wildlife Health project for monitoring
Avoid placing feeders where food residues remain and birds crowd closely together