A deadly disease responsible for a sudden decline in two of Britain's most popular garden birds has now spread to Europe. Trichomonosis, a disease normally associated with pigeons, apparently "jumped the species barrier" and began to affect British finches in 2005. In some areas chaffinch populations fell by a fifth and greenfinch populations by a third.
Now, research published in the journal EcoHealth suggests that chaffinches migrating from British shores to Scandinavia have carried the parasite that causes the disease, infecting birds there. Finches that had died from trichomonosis began to be found in Norway, Sweden and Finland for the first time in the summer of 2008.
The parasite, trichomonas gallinae, has long been known as a cause of disease in pigeons and doves, and in birds of prey that feed on them, but not hitherto in songbirds. It is vulnerable to dryness and cannot survive for long periods outside its host, so transmission of infection is most likely to be through birds feeding one another with regurgitated food during the breeding season; or through food or water contaminated with saliva.
Research carried out by the Zoological Society of London, the British Trust for Ornithology, the University of East Anglia, and other scientific organisations across Europe, suggests that chaffinches have taken the disease abroad.
Outbreaks of trichomonosis can occur at any time of the year but tend to peak during August and September, when sick birds stay close to feeders and sources of water, and often die there. Infected birds often look lethargic and have fluffed-up feathers. They may also show signs of struggling to feed and have trouble breathing.
The next priority, say the researchers, is to understand the spread and impact of this disease on bird populations across Europe.