You might see it before you know what it is. Warty growths on the legs, beak, or eyes of a bird. These are the hallmark of Avipoxvirus. It is a large DNA virus that infects a wide range of avian species, including many native New Zealand birds like tūī, bellbirds, and kiwi. The virus is transmitted by mosquitoes or through direct contact with infected birds or contaminated surfaces. The lesions can be unsightly and debilitating. If they block the eyes, the bird cannot see. If they obstruct the beak, it cannot eat. Secondary infections are common. In some cases, the disease is fatal. In others, the bird recovers, but the stress weakens it against other threats. The virus is particularly concerning for endangered species with small populations. An outbreak can have disproportionate effects. It is also a problem in urban gardens, where high densities of birds facilitate spread. Feeders and baths can become hotspots if not cleaned regularly. The virus persists in the environment. Mosquitoes, which are becoming more common as the climate warms, act as efficient vectors. Management focuses on hygiene and monitoring. Cleaning bird feeders and reducing mosquito breeding sites can help. But the virus is here. It moves with the wind and the wing. The bird with the warty leg hops on, unaware of the microscopic passenger it carries.