Impacts of disease become evident

Many garden feeders have been busy with young goldfinches and greenfinches over recent weeks, suggesting that these small birds might have enjoyed a good breeding season. This news has, however, been tempered by reports of fluffed up and lethargic looking individuals, indicating the presence of disease within the population. The timing of these disease reports is suggestive of finch trichomonosis, the disease that first emerged in 2006 in the West Midlands before turning up in Norfolk the following year. Figures from the BTO Garden BirdWatch (www.bto.org/gbw) show that the impacts of those initial outbreaks are still being felt, at least within greenfinches.

We know about the disease thanks to the work of the Garden Bird Health initiative, a collaborative project involving a number of different organisations, supported by bird food companies, government agencies and private individuals. By pairing BTO Garden BirdWatch volunteers with wildlife veterinarians, it was possible to set up a systematic network to record the occurrence of disease at different sites across the country. Birds found dead could then be examined post-mortem to determine the cause of death and to identify the role, if any, of a disease agent. The project revealed the impact of the trichomonosis outbreak on finches, notably greenfinch and chaffinch, identified the likely origin as spill over from woodpigeons (which carry the Trichomonas parasite) and established the likely route by which it then spread to Scandinavia and continental Europe.

The full, longer-term impacts of the disease in finches have just been published in a paper for which I was an author. Working with colleagues at the Institute of Zoology, the RSPB and elsewhere, we have revealed the extent of losses sustained by the British greenfinch population. As a result of the disease we have lost in excess of 1.5 million greenfinches, a quarter of our breeding population and something that has seen the population decline to levels that were more typical of the 1980s. What is not clear is what will happen next. As I have already mentioned, Trichomonas is present within our woodpigeon population, something that has not stopped it from increasing, so a species can live with the parasite. Perhaps, since this is a new disease in the greenfinch, it will reduce the population through this initial stage but, longer term, it will rumble on at a much lower level.

Having systematic monitoring in place, both of greenfinch populations and disease occurrence, is obviously important. The presence of a network like the Garden Bird Health initiative (which has now ceased for lack of funding) would provide an early warning system for disease in wild birds. With new and emerging diseases a real possibility, let’s hope more funding is secured soon.

Finch disease spreads

That Britain has an important role in the wider pattern of bird movements is particularly evident at this time of the year, as many species – both rare and common – are noted arriving and departing by birdwatchers. As the first of our wintering geese arrive, so the last of our summer-visiting warblers depart. The scale of these movements is sometimes more difficult to gauge, however, particularly when it comes to common and familiar species like Greenfinch, Goldfinch and Chaffinch.

It is easy to assume that these finches, together with our other ‘resident’ species, are here all year; after all, they fill our hedgerows and woods with song in the summer and make use of our garden feeders come winter. Thanks to the efforts of licensed bird ringers we know that many of our wintering Chaffinches and Greenfinches arrive here from elsewhere, and that some of our breeding Goldfinches leave Britain for a winter spent in France and Spain.

The degree to which our finch populations are connected with those elsewhere in Europe was brought home to me recently through a piece of work with which I was involved. For several years now, I have been studying the impacts of an emerging infectious disease in finches. This disease, caused by a protozoan parasite, is known as trichomonosis and was first seen in wild finches in 2005. During 2006 we had our first outbreak, centred on the West Midlands and the Southwest of England, but in 2007 we saw it hit East Anglia. Our work has shown the disease to have reduced the Greenfinch population in affected regions by a third and the Chaffinch population by a fifth. This is the first time that anyone has been able to document a population level impact in a widespread European bird resulting from an infectious disease.

Worryingly, in 2008 a case was diagnosed in Sweden, followed by others the same autumn in Finland and Norway. Working with vets at the Institute of Zoology in London and molecular biologists at UEA, we have found that the trichomonad parasites taken from these birds are identical. This implies that the parasites arrived in Sweden, Finland and Norway via birds that had migrated from Britain. By examining bird movements we have been able to demonstrate that the most likely candidate is the Chaffinch, individuals of which migrate from eastern England to these countries come spring. Wintering Greenfinches, on the other hand, tend to migrate between eastern England and western Norway, away from where recent cases have been seen. With a foothold in these northern European populations we may see the disease emerge elsewhere in Europe, as migratory individuals mix over time. More on the disease can be found at www.bto.org/gbw

Disease outbreak hits finches

I have received an increasing number of calls over recent weeks from garden birdwatchers concerned at the appearance of dead and dying finches. In most instances these reports have involved greenfinches and chaffinches but there have also been occasional reports involving other species. This is not the time of the year when we would normally see birds dying from common diseases like salmonella and e-coli (these are normally seen in late winter), which suggests a different source. Thanks to the efforts of researchers working on the Garden Bird Health initiative, we have discovered that the disease involved is trichomonosis. This disease is caused by a parasite and it has been documented in a range of bird species, most commonly in doves and pigeons (where it is more commonly known as ‘canker’). The disease was first recognised in finches in Britain last summer, when a small outbreak was noted but this summer the outbreak seems to be that much larger and this has caused some concern.

Individual birds showing signs of the disease appear lethargic, fluffed up and reluctant to move away from feeding stations. They may have difficulty swallowing and may drool saliva or regurgitate food, something which can cause the feathers around the bill to become wet. Although in captivity the disease can be treated, it is virtually impossible to treat wild birds with an effective dose of medication. This means that prevention is the only practical option and garden birdwatchers should aim to reduce the risk of disease transmission between birds by adopting sensible hygiene practices. These include keeping bird feeders and bird tables clean (with a disinfectant or detergent) and by insuring that clean, fresh water is available each day, provided in vessels that have been thoroughly cleaned. It has been suggested that you should stop feeding altogether if you find any sick or dying birds but I feel that it is better to feed birds at a clean feeding station than force them to move on and potentially feed elsewhere where no hygiene measures are in place.

Most of the reports that I have received so far have come from western and central England but we should be alert here, in Norfolk, to the possibility that the disease might arrive. The parasite itself cannot survive for long outside of the body and it appears to be transmitted through salival contamination of food and water. This may be why it has been more widespread this summer – with the dry conditions reducing the availability of drinking pools and forcing more birds to congregate at those which remain.  More information on the disease and on sensible hygiene measures can be obtained from the British Trust for Ornithology and UFAW.