From late 2005, we began to receive reports of dead or dying Greenfinches, cases that were subsequently linked to an emerging infectious disease called Trichomonosis. This disease was already known from pigeons and doves but cases in wild finches were unknown. During the outbreak that followed (notably during 2006 and 2007) significant numbers of Greenfinches and Chaffinches died. In areas where the outbreaks were most pronounced we saw Greenfinch and Chaffinch populations decline by 35% and 21% respectively, representing mortality in excess of half a million birds.
Other species have been infected including Goldfinch, Bullfinch, House Sparrow and Tawny Owl. Only last week we had a report of a ringed Tawny Owl that had to be put to sleep due to necrotic Trichomonosis in the throat.
Unfortunately in 2008 Trichomonosis was discovered in Fennoscandia and was the likely result of migrating Chaffinches carrying the disease from the UK.
During the year there used to be a particular peak in reported cases during the autumn, due to the warm wet weather helping the parasite survive outside its host. More recently this trend is much less distinct. The reason for this is not fully understood.
Thanks to Jill Pakenham for the photo.