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.
Pathology & disease spread:
Trichomonas typically causes disease at the back of the throat and in the gullet. Affected birds show signs of general illness (lethargy, fluffed-up plumage) and may show difficulty in swallowing or laboured breathing. Some individuals may have wet plumage around the bill and drool saliva or regurgitate food that they cannot swallow. In some cases, swelling of the neck may be evident. The disease may progress over several days or even weeks.
The trichomonad parasite is vulnerable to desiccation and cannot survive for long periods outside of the host. Transmission is most likely to be through contaminated food or water, e.g. where a bird with difficulty swallowing regurgitates food that is then eaten by another individual. Trichomonas gallinae is a parasite of birds and does not pose a health risk to humans or their mammalian pets.
BTO researchers, working alongside others involved in the Garden Bird Health initiative, used Garden BirdWatch and other data to establish the impact of this disease on Greenfinch and Chaffinch populations. The results of this work revealed a substantial population decline in those areas where disease incidence was greatest. Find out more about this work and read the paper.
What you can do:
Follow sensible hygiene precautions as a routine measure when feeding garden birds and handling bird feeders and tables. Clean and disinfect feeders and feeding sites regularly. Suitable disinfectants that can be used include a weak solution of domestic bleach (5% sodium hypochlorite) or other specially-designed commercial products. Always rinse feeders thoroughly and air-dry before re-use.
Rotate positions of feeders in the garden to prevent the build up of contamination in any one area of ground below the feeders. Empty and air dry any bird baths on a daily basis. You may wish to consider stopping feeding if you have an outbreak of the disease at your feeding station, in an attempt to force the birds to feed elsewhere at a lower density (although in reality they may end up visiting another feeding station and possibly one where no hygiene measures are in place.
If you wish to report finding dead garden birds, or signs of disease in garden birds, you can do so through Garden Wildlife Health, our online reporting system.
What effect might annual releases of non-native gamebirds be having on native biodiversity?
Henrietta Pringle reveals the work behind a recent paper on gamebirds and predation
Climate change in a warming world
BTO science contributes to our understanding of future scenarios, and informing policies and conservation management strategies to help species adapt.