An adult Greenfinch displaying typical symptoms of trichomonosis.
Photo attribution: Chris / The last of the Greenfinches: Yarburgh 2010 /CC BY-SA 2.0
What is trichomonosis?
Garden bird trichomonosis is a disease caused by the protozoan parasite Trichomonas gallinae, which causes lesions in the gullet, preventing swallowing of food and water. Therefore, affected birds often become emaciated and may die of starvation. This parasite is thought to be spread via regurgitated food and fresh saliva, both directly (through birds feeding each other, such as parents feeding young) and indirectly (by consuming contaminated food or water).
For many decades, garden bird trichomonosis was mainly observed in pigeons and doves, and birds of prey feeding on them. However, this changed in 2005 when increasing numbers of sick and dead songbirds (mainly Greenfinches and Chaffinches) began being reported from residential gardens in Great Britain. Trichomonas gallinae was found to be the cause and the disease was rapidly spreading through finch populations. Since becoming epidemic in Greenfinches and Chaffinches, the disease has led to population declines of 62% for Greenfinch and 37% for Chaffinch (2011-21), resulting in Greenfinches being added to the UK Red List of birds of conservation concern. Trichomonosis has been observed in several other garden bird species, although finches appear particularly at risk. For both Chaffinch and Greenfinch there is evidence of reduced survival in suburban compared to rural areas, suggesting a possible link to gardens and supplementary feeding.
Greenfinch
Chaffinch
Changes in the relative abundance of Greenfinch (Chloris chloris) and Chaffinch (Fringilla coelebs) in the UK (1994-2021). Source: BTO/JNCC/RSPB Breeding Bird Survey
New study aims to improve understanding of finch trichomonosis transmission and mitigation measures
Our new study is a collaboration between the RSPB, British Trust for Ornithology (BTO) and Institute of Zoology (IoZ), with funding from Natural England (NE), which aims to improve our understanding of the factors involved in finch trichomonosis outbreaks in garden situations and to learn more about how we can reduce disease risks and improve mitigation measures. One key aspect of the study involves RSPB scientists visiting gardens with active outbreaks of suspected finch trichomonosis to collect data and samples that will help establish how transmission occurs and what situations might present a high risk.
How you can help!
Signs of trichomonosis in garden birds
In addition to showing general signs of illness like lethargy and fluffed-up plumage, affected birds may drool saliva, regurgitate food, have difficulty in swallowing or show laboured breathing. Finches are frequently seen to have matted wet plumage around the face and food stuck to their beak.
For example images, see GWH website symptom identifier
Wildlife disease surveillance relies on people reporting sick and dead wildlife promptly, and for this new study, we are particularly looking for gardens with an active outbreak of finch trichomonosis. If you see sick or dead Greenfinches or Chaffinches showing signs of possible trichomonosis (listed below) and would be interested in participating, please do not change your feeding and watering practices* and report the incident to the Garden Wildlife Health (GWH) website at your earliest convenience. The GWH wildlife vets will then get back to you rapidly to discuss the requirements for the study in detail. Please do not handle sick or dead birds directly. Should movement of a carcass be required, please see the GWH website for more information.
Further information on this important infectious disease in garden birds can be found here: GWH Garden Bird Trichomonosis Factsheet
Should you observe sick or dead garden birds that do not fit the above description or you do not wish to participate in the study, please still report the incident through the GWH Reporting Portal - every single report is invaluable in helping us to learn more about the health of British garden wildlife. GWH wildlife vets will subsequently provide further advice. Further information on best-practice for garden bird feeding and disease mitigation can be found in our collaborative Feeding Guidelines.
If you find five or more dead wild birds of any species in the same location at the same time, or one or more dead birds of prey, gulls, swans, geese or ducks, please report this directly to the Government’s avian influenza surveillance portal at www.gov.uk/guidance/report-dead-wild-birds.
Please be aware that garden birds can be affected by various disease conditions, and whilst the risks are low, some may have the potential to affect humans or domestic animals. Therefore, we recommend always following strict hygiene precautions when interacting with wildlife, such as wearing gloves, not handling sick or dead wildlife directly, and always washing your hands thoroughly.
If you have concerns or questions about wild bird disease, please contact RSPB Wildlife Enquiries:
Phone: 01767 693690 or Email: wildlife@rspb.org.uk
*We recognise that this request goes against current best-practice advice of withdrawing supplementary food and water in cases of garden bird trichomonosis being suspected, but in order to improve our understanding and to ultimately help prevent disease outbreaks, it is essential for us to collect information before food and water is removed. We are aiming to collect this necessary data within a few days and only from a small number of gardens, after which removal of food and water as a disease control measure should be implemented.
Further Reading
Robinson, R.A. et al. (2010) Emerging Infectious Disease Leads to Rapid Population Declines of Common British Birds. PLoS ONE 5(8): e12215. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0012215
Lawson, B. et al. (2012) The emergence and spread of finch trichomonosis in the British Isles. Philos. Trans. R. Soc. B Biol. Sci. 367, 2852–2863 https://royalsocietypublishing.org/doi/10.1098/rstb.2012.0130
Hanmer, H.J. et al. (2022) Habitat-use influences severe disease-mediated population declines in two of the most common garden bird species in Great Britain. Scientific Reports, 12(1), 15055. https://doi.org/10.1038/s41598-022-18880-8
Electron microscope image of the protozoan flagellate Trichomonas gallinae (from Robinson et al. 2010) CC BY-SA 4.0