Trichomonosis insight

The impact that diseases have on bird populations is a fascinating topic of research, to which ringers and members of the public can contribute. Many will now be aware of the detrimental effect that Trichomonosis has had on Greenfinch populations in the UK, a relationship established by a piece of research led by scientists at the Institute of Zoology in London and the BTO. A subsequent study from the same team also showed, through molecular analyses, that the disease arrived in Fennoscandia from the UK in 2008, most likely carried by Chaffinches. This link was identified thanks to the known migration route of this species provided by previous ringing data.

Greenfinch showing signs of Trichomonosis by Heather Povey

A project by different authors has recently showed that Trichomonosis spread in Finland in 2008 and 2009 and impacted local Greenfinch and Chaffinch breeding populations. In August-September 2008 the first cases of this disease had appeared in the country, followed by a peak in reported mortality in July 2009, although cases diminished in 2010 to pick up again in 2011. The Finnish study showed that population of breeding Greenfinch declined by 47% in south Finland, but not other parts of the country, at the peak of the outbreak between 2009 and 2010, whilst Chaffinch declined by 4%, between 2006 and 2010, the first population decrease since 1984. Bird body condition was also affected by the disease. Ringing data highlighted that Greenfinches, especially juveniles, were lighter than usual over the autumns 2008 and 2009 in the areas most affected by Trichomonosis.

These studies are a very good example of the important contribution to science that members of the public and ringers provide by reporting changes in birds and garden wildlife, as well as the unique high-quality data and essential information that ringing provides.

For more background information, visit the BTO GBW webpage

Daria Dadam, Research Ecologist

Tricky Customer

From late 2005, we began to receive reports of dead or dying Greenfinches, cases that were subsequently linked to an emerging infectious disease called Trichomonosis. This disease was already known from pigeons and doves but cases in wild finches were unknown. During the outbreak that followed (notably during 2006 and 2007) significant numbers of Greenfinches and Chaffinches died. In areas where the outbreaks were most pronounced we saw Greenfinch and Chaffinch populations decline by 35% and 21% respectively, representing mortality in excess of half a million birds.


Other species have been infected including Goldfinch, Bullfinch, House Sparrow and Tawny Owl. Only last week we had a report of a ringed Tawny Owl that had to be put to sleep due to necrotic Trichomonosis in the throat.


Unfortunately in 2008 Trichomonosis was discovered in Fennoscandia and was the likely result of migrating Chaffinches carrying the disease from the UK.

During the year there used to be a particular peak in reported cases during the autumn, due to the warm wet weather helping the parasite survive outside its host. More recently this trend is much less distinct. The reason for this is not fully understood.

Thanks to Jill Pakenham for the photo.

Greenfinch control comes full circle

The Ringing Office has very extensive paper archives, but storage space is running out, so we are disposing of old recovery letters more than 20 years old. However before disposal we are removing and keeping any attached rings and also keeping samples of all the letters.


A happy coincidence recently was when a volunteer came across a 'BRC16' reporting a Greenfinch control from Dec 1987 in Ireland of a bird which our Ringing Database Officer Dorian Moss had ringed in his garden in Anglesey a few months earlier.


View Dorians Greenfinch recovery in a larger map

The Migration Atlas shows that movements of Greenfinches across the Irish Sea are relatively unusual, so it was rewarding to be reminded of this interesting control.