UK Nature and Environment

Back when the RSPB’s Big Garden Birdwatch began in 1979, the Greenfinch was at number seven in the top 10 birds seen. But in this year's Birdwatch (2026), they were down to number 18. These figures reflect a broader loss across the UK. Numbers of Greenfinches have been falling since around 2005, dropping by over 65% in the last three decades.

In 2021, conservationists moved Greenfinches into the Red List category in the Birds of Conservation Concern report due to this severe decline. Chaffinch numbers have begun to decrease too, with 39% being lost between 2012 and 2022. For both species, the cause is a disease, trichomonosis.

Trichomonosis is caused by a microscopic protozoan parasite called Trichomonas gallinae. It typically infects the upper digestive tract of birds. Trichomonosis has been known to affect pigeons and doves, along with birds of prey, for many years. These bird species can be infected by different strains of the parasite, they can act as carriers or succumb to the disease.