Why are the birds getting sick?
Birds use up a lot of energy and resources in spring and summer building nests and raising young, so by the end of summer they are often very run down. Like in humans, this can lower their immune system and make them more vulnerable to infections. Disease risk is further increased by the fact that most birds are generally far less territorial after the breeding season and tend to flock together at feeding sites, which greatly increases the chance of a disease spreading between individuals.
Apart from finding corpses, what should you look out for?
Different illnesses cause different symptoms. General signs of illness include lethargy and slower reactions, and sick birds often fluff up their feathers in an attempt to conserve energy.
Avian pox - a viral skin infection that causes warty growths, most commonly on the head and neck. Often seen in tits, dunnocks and pigeons.
Trichomonosis - caused by a parasite that lives in the digestive tract of birds. Infected individuals have problems swallowing and will often have food and saliva around their beak and face. Often seen in finches, doves and pigeons.
What can I do to help a sick bird?
Unfortunately, wild birds cannot be treated for disease because it is too difficult to ensure that the medicine goes to the right birds in the right dosages. It is also difficult to diagnose a bird from observation alone. Birds that can be caught easily are usually too ill to recover but you may wish to contact the RSPCA or your local vet.
If you notice dead or sick birds in your garden, the best thing you can do is to temporarily stop feeding them. If there is disease in the local population, you do not want to encourage birds to congregate together in your garden as this will allow the disease to spread to healthy individuals. Wear protective gloves to remove and disinfect all feeders, bird tables and bird baths, and wash your hands thoroughly as soon as you've finished. Once you stop seeing dead/sick birds, you can start feeding again.
Help scientist study garden bird disease by reporting any suspected outbreaks on the Garden Wildlife Health website.