In the UK, garden bird feeding is one of the most popular and common forms of human-wildlife interaction, especially within highly built up areas. This practice began to try and assist garden bird survival in the wild during the harshest months of the year. It ended up benefiting humans too, as it allowed us to observe multiple species of bird from the comfort of our own homes. Despite this benefit, many scientists and bird enthusiasts have become concerned that birds could become reliant on bird feeders/tables. Many birds together in one place also means that disease, mites and parasites are more likely to spread. One such parasite is Trichomoniasis. The UK greenfinch population has dropped by one fifth since 2005, directly as a result of Trichomoniasis and is directly correlated with the increase of bird feeding.
What is Trichomonosis?
Trichomonosis is caused by an infection from a parasite called Trichomonas gallinae. The infection of the parasite causes lesions in the back of the throat and sinuses of the bird. The growth of the lesions restricts and blocks the throat so that the bird cannot eat or drink, resulting in its death from starvation or dehydration. It was originally identified in pigeons and doves but has adapted to infect other avian hosts. Outbreaks of the disease are more likely between August to October.
Trichomonas gallinae is a protozoan organism (a single-celled organism) belonging to a group of organisms called flagellates. The protozoan reproduces by replication called longitudinal fission, meaning it divides itself in two. It does not produce a long living oocyst (essentially a capsule-like an object that allows the organism to live outside of its host) like other protozoan species. Therefore, it is not capable of surviving away from its host. Even so, it can live for a very short period of time within moist debris before it infects an individual. Within its host, it lives and feeds on the internal mucosal surfaces of the body, mainly the upper gastrointestinal tract (oesophagus, crop and proventriculus), mouth, throat region and upper respiratory tract. The parasite is present within the mouth, nose salvia, and faeces of its host allowing it to infect other individuals.
How Does it Infect Birds?
Trichomonosis can be passed via a mother bird’s salvia – they can then infect their young through the regurgitation process. They can pass it on to other birds via contaminated food, water and bedding. It can even be passed on during courtship by to beak-to-beak contact. Adult birds can carry the disease for over a year without showing any signs of infection, while continuously infecting all birds in contact with them.
Symptoms of Trichomoniasis
- Loss of appetite;
- Weight loss;
- Dull appearance;
- Difficulty standing;
- Mouth open;
- Difficulty breathing and swallowing; and
- The neck may appear puffy (puffed up plumage).
It is important to remember that birds fluff up their plumage during the winter months, so a bird may not be ill – just cold!
Can humans get Trichomoniasis?
Humans cannot get avian Trichomonosis. It is highly contagious amongst birds but does not infect other wildlife or humans.
Is There a Cure?
If exotic bird pets get this disease then the following medication has been used to treat them: metronidazole, ronidazole, carnidazole and dimetridazole, and has done so successfully. However, for birds in the wild, using drugs is not a practical or cost-effective way to treat bird populations; preventative measures are far more effective.
How Many Bird Species Have Been Affected?
The first British garden birds that were identified with the parasite were within the greenfinch and chaffinch populations during 2005. Large scale mortality of these species occurred in 2006. By 2007, 500,000 greenfinches were killed by the disease and as a result, the greenfinch population declined from 4.3 million to 2.8 million birds. The number of greenfinches visiting gardens has also decreased by 50%! Although chaffinch populations were also initially affected by the disease, their populations have remained stable.
It has been suggested, from a close scientific study of the disease, that Trichomonosis spread to the finch populations by jumping from columbiform species (pigeons) to passeriform (small garden birds). Further investigation is needed to better understand how protozoal diseases can jump from one host taxonomic group to another in a very short period of time.
Is this Affecting Bird Conservation?
Although the majority of the reported cases of Trichomonosis have been identified in greenfinches and chaffinches, a small number of cases have been identified in other species of birds, for example, house and tree sparrows, pheasants, and multiple birds of prey. Even so, the more common passerines in our gardens such as robins and blackbirds have not yet contracted the disease and appear to be immune.
This disease is having a detrimental impact to bird populations across Europe – not just the UK. In the UK, it is believed that chaffinches are the main carriers of the disease as they migrate to other unaffected areas of the UK, infecting multiple species of passerines as they go.
But we can do something about this! Just by disinfecting your bird feeders and tables regularly, you can prevent the spread of this disease in our bird populations and prevent the spread of mites and leg lesions too. The bird feeders should be moved to different locations around the garden to prevent the build-up of waste that could harbour the disease. Drainage holes in your bird feeders or bird tables are also a useful way to try and reduce the build-up of moisture.
If you come across a garden bird with the disease then all bird feeding should be stopped, all feeders and tables should be cleaned and air dried. Do not put food out for the birds for at least 10 to 14 days so that the regular bird visitors can disperse, thus reducing the likelihood that those that have been infected will infect healthy birds. Only resume bird feeding when you can no longer identify sick individuals.
See our handy guide opposite on cleaning bird feeders and bird baths adjacent, which is based on advice given by both the BTO and the RSPB:
Take a look at this video to learn more about garden birds!
Enjoyed reading this article? Then why not read our other wildlife disease blogs:
- Samour, J.H., Bailey, T.A. and Cooper, J.E., 1995. Trichomoniasis in birds of prey (Order Falconiformes) in Bahrain. The Veterinary Record, 136(14), pp.358-362.
- Lawson, B., Cunningham, A.A., Chantrey, J., Hughes, L.A., John, S.K., Bunbury, N., Bell, D.J. and Tyler, K.M., 2011. A clonal strain of Trichomonas gallinae is the aetiologic agent of an emerging avian epidemic disease. Infection, Genetics and Evolution, 11(7), pp.1638-1645.
- Robinson, R.A., Lawson, B., Toms, M.P., Peck, K.M., Kirkwood, J.K., Chantrey, J., Clatworthy, I.R., Evans, A.D., Hughes, L.A., Hutchinson, O.C. and John, S.K., 2010. Emerging infectious disease leads to rapid population declines of common British birds. PLoS one, 5(8), p.e12215.
- Jones, D.N. and James Reynolds, S., 2008. Feeding birds in our towns and cities: a global research opportunity. Journal of avian biology, 39(3), pp.265-271.
- Lawson, B., Robinson, R.A., Neimanis, A., Handeland, K., Isomursu, M., Agren, E.O., Hamnes, I.S., Tyler, K.M., Chantrey, J., Hughes, L.A. and Pennycott, T.W., 2011. Evidence of spread of the emerging infectious disease, finch trichomonosis, by migrating birds. Ecohealth, 8(2), pp.143-153.
- Lawson, B., Robinson, R.A., Colvile, K.M., Peck, K.M., Chantrey, J., Pennycott, T.W., Simpson, V.R., Toms, M.P. and Cunningham, A.A., 2012. The emergence and spread of finch trichomonosis in the British Isles. Philosophical Transactions of the Royal Society of London B: Biological Sciences, 367(1604), pp.2852-2863.
- Galbraith, J.A., Stanley, M.C., Jones, D.N. and Beggs, J.R., 2017. Experimental feeding regime influences urban bird disease dynamics. Journal of Avian Biology, 48(5), pp.700-713.
Author: Ashley Dale