1. Disease: Trichomonosis
Disease in garden birds has become a big issue in recent years, and the BTO has been involved heavily in this research.
The disease which has received the most coverage has been trichomonosis and its impact on finches – particularly greenfinches and chaffinches.
John Harding 1

2. Finch trichomonosis Typical symptoms: fluffed up lethargic
Image © Heather Povey
Typical symptoms:
fluffed up
lethargic
trying to feed
difficulty swallowing
“messy face”
Trichomonosis is caused by a protozoan parasite, where lesions in the gullet develop and subsequently lead to difficulty in swallowing. The birds often appear fluffed up, lethargic and have a messy face. The parasite is spread via fresh saliva, and can be transmitted when birds feed one another directly, for example during the breeding season, or at shared food and water sources. This means that the parasite may be spread between birds using garden feeders and bird baths.
Heather Povey
BTO Garden BirdWatch 2

3. Finch trichomonosis BTO Garden BirdWatch
Daily Mail, 2006
Trichomonosis emerged as novel, often fatal, disease of finches in 2005.
The disease rapidly became epidemic in greenfinches, and to a lesser extent in chaffinches, during 2006, and is still the most commonly diagnosed infectious disease in British garden birds.
This research relied on the observations of Garden BirdWatchers and has been published in peer-reviewed scientific journals.
Photos: left = post mortem examination of a diseased bird – typical picture of a lesion in the gullet of a greenfinch, caused by Trichomonas gallinae. Post-mortem examination and detection of the parasite are necessary to confirm the cause of death. Top right = Trichomonas gallinae parasite under electron-microscope. Low right = the severe population decline of greenfinches received lots of media coverage and public concern.
Robinson et al. (2010) PLoS ONE
BTO Garden BirdWatch
Robinson, Lawson, Toms, et al. (2010): PLoS One 3

4. Greenfinch decline BTO Garden BirdWatch
Trichomonosis has now caused a decline of around 50% of the breeding population of British greenfinches since it emerged in It is estimated that this represents the deaths of over 1.5 million birds and we understand it is the largest scale mortality of wild birds due to infectious disease in Great Britain. This highlights the potential for disease to be of important for conservation as well as animal welfare.
BTO Garden BirdWatch 4

5. Lawson et al (2011) Ecohealth
Finch trichomonosis
Transmission ?
Image ©Josie Latus
How is trichomonosis transmitted and how has it spread?
The trichomonas parasite has been known to infect and cause disease in pigeons and doves, and birds of prey for hundreds of years. The disease emerged in finches in 2005 and we believe this occurred as a result of a species jump from a pigeon or dove to a finch in Great Britain.
In 2008, trichomonosis was first seen in finches in southern Fennoscandia. Molecular analyses showed the strain of trichomonas parasite was the same as in the UK.
Chaffinches make large annual movements to and from the UK, particularly from Sweden and Norway but also Finland and Russia, during autumn and spring. Through studies of bird migration and disease spread, we believe that Chaffinch migration is most likely to be responsible for the easterly spread of finch trichomonosis to Fennoscandia.
Again, this research incorporated the observations of Garden BirdWatchers and was published in a peer-reviewed scientific journal.
Finally, there is some evidence to support a population decline of sparrowhawks over the past decade. Since sparrowhawks are common garden visitors, which rely on songbird prey, it is possible that they may have predated finches suffering from trichomonosis. Unfortunately the parasite can pass up the food chain and cause disease in birds of prey that predate or scavenge them. Whilst we cannot be sure, there is a hypothesis that finch trichomonosis may also have contributed to the observed population decline of this bird of prey. Another important infectious disease affecting garden birds is avian pox. However, this disease has an impact on animal welfare of individual birds rather than on a population level. ?
Image © Sarah Kelman
Lawson et al (2011) Ecohealth
BTO Garden BirdWatch
Lawson, Robinson et al. (2011): EcoHealth
John Harding 5

6. Disease: Avian Pox Image © Roy Norris
Another important infectious disease affecting garden birds is avian pox. However, we believe this disease has an impact on animal welfare of individual birds rather than on a population level.The disease affects a wide variety of bird species around the world. Sporadic cases of avian pox have been recorded for decades affecting species such as the dunnock, house sparrow, starling and wood pigeon.
However, a severe form of avian pox was first observed in tit species in 2006 and this is a new and emerging condition in Great Britain. Whilst a range of tit species appear susceptible to the disease, great tits are most frequently and severely affected.
Image © Roy Norris

7. Avian Pox Typical symptoms: Growths on head, body, feet
Image © David Wragg
Image © Tony Kelly
Birds with avian pox develop warty or tumour-like growths, on the head (particularly next to the eye or beak), legs, wings, or other body parts. The growths can become very large and may impede the ability of birds to see, feed or move around. In these cases the birds become more susceptible to predation. Whilst the disease in great tits is not invariably fatal, and recovery can occur, the condition reduces individual survival, particularly in juvenile birds.
Typical symptoms: Growths on head, body, feet
Andrew Cannon
BTO Garden BirdWatch 7

8. Avian pox in Great Tits 2008 2013-2017 2010 BTO Garden BirdWatch
Avian Pox DIRs
2010
Tony Kelly
The distribution of reports of avian pox in tit species show that the disease was first seen in south east England, and has since spread north and westward across England and Wales. This pattern is consistent with the virus being introduced into England from mainland Europe, where the disease has previously been seen in great tits.
Andrew Cannon
Lawson et al. (2012) Emergence of a novel avian pox disease. PLoS One 7 (11): e40176
BTO Garden BirdWatch 8

9. Avian pox in Great Tits Transmission BTO Garden BirdWatch
Tony Kelly
Avian pox virus can be spread through direct and indirect contact between birds or via an arthropod vector like a mosquito. Since great tits are not a migratory species, we believe the disease is most likely to have been introduced to GB by movement of an infected insect vector.
Andrew Cannon
BTO Garden BirdWatch 9

10. Finch leg lesions Viral cause: Papilloma virus
Tony Kelly
The GWH project frequently receives reports of chaffinches with leg abnormalities associated with a mite infestation (Cnemidocoptes) and/or infection with chaffinch papillomavirus. 
Most commonly, affected birds remain bright and active. However, more severe cases do occur which can interfere with locomotion and predispose them to predation.
Viral cause: Papilloma virus
Parasitic cause: Mites (Cnemidocoptes)
Andrew Cannon
BTO Garden BirdWatch 10

11. Public Health BTO Garden BirdWatch
Tony Kelly
Passerine salmonellosis is another infectious disease that we used to commonly diagnose in the seed-eating songbirds, such as house sparrows and greenfinches, particularly during the winter months. Whilst the condition does still occur the number of confirmed cases has dropped significantly in recent years. There are many types of Salmonella bacteria but garden birds are affected by particular strains that we believe are adapted to these wildlife species. Salmonella bacteria are spread through bird droppings and have the potential to affect humans, leading to food poisoning-like symptoms. Therefore hygiene precautions are recommended as routine, for example cleaning bird feeders outside in a bucket and not handling sick or dead garden birds directly. However, studies have shown that these garden bird strains of the bacterium represent only 0.2% of human salmonella infections so the risk should be kept in perspective. Cats can also become infected when they predate sick birds with the condition.
BTO Garden BirdWatch 11

12. “What can I do…?” www.gardenwildlifehealth.org
Tony Kelly
What can you advise to someone who has a general question on GWH? First suggest they explore the GWH website, encourage people to report observations to gain an informative reply, and when in doubt – give the GWH veterinarians a call or simply send an !
When in doubt – contact us:
BTO Garden BirdWatch 12

13. Thank you! Any questions? Image © Tommy Holden
Image: Jill Pakenham / BTO