The few occassional broken tail feathers or a few feathers missing from above the beak, aswell as a generally untidy plumage are not exact indicators of disease. Most usually they are due to a moult or general wear and tear i.e. fighting between pairs (completely normal- they all fight even if they have bonded and reared chicks) or bumps and scratches from branches in the aviary, which will cause ragged feathers. Only if the Blackbird looks fluffed (not to be confused with the fluffing during rest), lethargic, is not eating or is constantly huddled on the aviary floor, should you take the bird to the vet.

The most common potential ailments which Blackbirds are susceptible to are intestinal worms, mites and lice. So the birds should recieve Expel wormer every 4 months and anti-mite/lice spray as and when needed.