Garden BirdWatchers allow us to better understand disease in British finches

Chaffinch by Jill Pakenham

Leg lesions, more commonly known as ‘scaly leg’ or ‘tassel foot’ are growths on the legs of feet of finches. A study from the Zoological Society of London in collaboration with BTO, the Complutense University of Madrid and Linnaeus University, explores the causes, seasonality and distribution of one of the most notable diseases in wild birds in Britain.

Leg lesions, more commonly known as ‘scaly leg’ or ‘tassel foot’ are growths on the legs of feet of finches. A study from the Zoological Society of London in collaboration with BTO, the Complutense University of Madrid and Linnaeus University, explores the causes, seasonality and distribution of one of the most notable diseases in wild birds in Britain.

Leg lesions are one of the most commonly seen signs of ill health in British birds. Results from post-mortems on over a thousand finches have found that these leg lesions have two causes; a virus (Fringilla coelebs papillomavirus) and mites (Cnemidocoptes). The most frequently affected birds are Chaffinches but leg lesions have also been documented in other finch species.

Weekly reports from BTO Garden BirdWatchers, as well as ad hoc sightings of disease from members of the public to Garden Wildlife Health, show that leg lesions in finches are widespread across the UK. However, reports of leg lesions increase during the winter period between November- March, at a time when we see an influx of Chaffinches from the continent, joining our breeding birds. The increase in migratory finches at this time might help to explain the increase in disease reporting rate in the winter months.

We know that leg lesions, whilst distressing to see, often do not impede the birds and most of the time they behave normally, but in severe cases birds can become lame and will be increasingly vulnerable to predation. Currently there is no evidence that leg lesions pose a threat to conservation of wild finches. 

You can help reduce the spread of the disease in your garden by following good hygiene measures when feeding garden birds, such as regularly cleaning your feeders.  For more information on how to prevent disease and to report disease in your garden see the Garden Wildlife Health website.

Related publications:

Lawson, B., Robinson, R.A., Rodriquez-Ramos Fernandez, J., John, S.K., Benitez, L., Tolf, C., Risely, K., Toms, M., Cunnigham, A.A. & William, R.A.J 2018
Spatio-temporal dynamics and aetiology of proliferative leg skin lesions in wild British finches Scientific Reports.
Link to publication (DOI: 10.1038/s41598-018-32255-y).

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