There’s hardly a mention of the Greenfinch without reference to Trichomonosis (Trichomonas gallinae). But what is it?
Trichomonosis is a virulent parasitic infection that has been notable in the recent, sharp declines of, primarily, Greenfinches and Chaffinches, although the disease has affected other garden bird species such as pigeons, House sparrows, Dunnocks, Great tits and Siskins.
Affecting the back of the throat and the gullet, making it difficult for Greenfinches to feed, Trichomonosis can cause excessive salivation and vomiting, which means the disease can spread relatively easily while birds are feeding on feeders. The disease spreads dramatically throughout the breeding season when parent Greenfinches feed their young.
It is therefore essential to keep feeders and bird baths clean if your garden attracts Greenfinches to prevent, as much as possible, the disease from spreading. Once cleaned, allow your feeders to dry out thoroughly before using again, as the process of drying can kill the infection. Trichomonosis cannot survive for long outside the host.
Due to the different migratory routes taken by Greenfinches and Chaffinches: Greenfinches migrate directly to and from Northern Europe over both seasons, whereas in Spring the Chaffinch diverts via Germany, Denmark and Belgium, thus increasing the likelihood that Trichomonosis was spread in mainland Europe by the Chaffinch.