Tuberculosis in birds is caused by a certain type of bacteria. This disease can be contracted through infected food, stings or bites, wounds, or from inhalation.
The disease usually enters the lungs. Here it is stopped by the body's defense system. Around the bacteria the defense cells form a hard, calcified mass to prevent it from spreading. This takes up lung space which results in weakness. The weaknes would keep the bird from flying, and getting to food and away from danger are harder, and because of this death could result.