New virus hits Great Tits

The arrival of a new strain of avian pox has been in the news of late, thanks to the publication of a piece of research with which I was involved. The sight of any diseased bird can prove distressing but to see one with a huge growth covering part of its face is particularly upsetting. This, unfortunately, is what we have been seeing over the last few years in some of our Great Tits and it seems likely that we will see more individuals suffering from this virus as it spreads further across the country.

Avian pox is a familiar enough sight, with small lesions not uncommonly reported from Blackbirds, House Sparrows and Dunnocks, among others. This strain of pox virus is less severe and birds often recover. That recently found in British Great Tits is far more unpleasant and the large growths can restrict vision and movement, making the birds more prone to predation and to secondary infection.

My work at the BTO, carried out in association with vets at the Institute of Zoology, researchers at the RSPB and at the Edward Grey Institute in Oxford, has revealed that the virus being seen in our Great Tits is the same as that found in certain continental populations in the past. Not only that, but we have been able to trace its spread since the first case was diagnosed in 2006. Using information collected by BTO Garden BirdWatchers, who keep a weekly count of the birds and other wildlife using their gardens, we have been able to document the disease as it has crept northwards across the UK from an origin somewhere near the south coast. The pattern of arrival, coupled with our knowledge of Great Tit movements, underlines that the virus was almost certainly transported here by a biting insect, possibly a mosquito. British Great Tits are largely sedentary in their habits so it is very unlikely to have arrived via an already infected bird.

You may recall the arrival of blue tongue disease in East Anglia and the link to the continent via a plume of warm from the south bringing with it the biting midges that transport the disease. Something very similar may have happened in the case of the avian pox that we are seeing in these unfortunate Great Tits. Transmission between birds is primarily via biting insects but the virus may also be spread by bird-to-bird contact or via contaminated surfaces, so you should maintain suitable hygiene practices around your garden feeding stations. Hanging feeders and bird tables should be washed weekly, using disinfectant before being rinsed and then air-dried. If you see lots of diseased birds then consider ceasing feeding altogether for a few weeks.