Trichomonosis is the name given to a disease caused by the protozoan parasite Trichomonas gallinae. It has been recorded in a number of garden bird species and is widely acknowledged to be the causal factor in the rapid decline of the British Greenfinch population that was first noted in late summer 2006. The disease is also known as ‘canker’ when seen in pigeons and doves, and as ‘frounce’ when seen in birds of prey. It has been known as a disease of cage birds for some time.
Although known from pigeons, doves and birds of prey for some time, the disease came to prominence in summer 2005, when it was first noted in British finches. Epidemics of the disease occurred in 2006 and 2007, with smaller scale mortality events noted in subsequent years. Greenfinches and Chaffinches are the species that have been most frequently affected, but the disease has also been documented in other garden bird species, including House Sparrow, Dunnock, Great Tit and Siskin.