According to this article our garden birds are currently being hit by an avian pox virus. The virus which leads to warty tumour like growths on birds has been affecting a wide range of birds including dunnocks, house sparrow, starlings and wood pigeons. The worst affected birds, however, seem to be great tits which seem to suffer from much more severe infections. Conservationists are calling for member's of the public to help track the spread of the disease by looking out for birds with symptoms and reporting them to the RSPB Wildlife Enquiries Unit on 01767 693690. It is thought the virus is spread through direct contact between birds and also indirect contact via perches and bird feeders where the birds congregate. You can help by keeping any bird tables and birds feeders disinfected to try and prevent the spread of any disease.