The greenfinch declined 67% between 2005 and 2020, primarily due to trichomonosis — a parasitic disease spread at garden bird feeders. This represents one of the clearest examples of human feeding practices causing welfare harm.
Greenfinch welfare was catastrophically affected by trichomonosis spread at garden feeders — an entirely human-facilitated welfare crisis. Infected birds experience a distressing death: oral lesions prevent swallowing, birds become progressively thinner over 1-2 weeks before dying. The disease spreads when infected birds contaminate food with saliva or droplets. Strict feeder hygiene — weekly disinfection, removing all wet or stale food, and using feeder types that minimise saliva contamination — can reduce disease transmission. The greenfinch decline demonstrates that garden bird feeding, while generally beneficial, requires responsible management to avoid causing the very harm it intends to prevent.