Most birds have four paired air sacs and one single air sac that connect to the lung and help create a large respiratory capacity. Birds affected this way might have a voice change followed by severely labored breathing. Affected birds will often breathe through their mouth and stretch out their necks in an attempt to breathe. Death may occur in a matter of days. As the fungus spreads through the lungs and air sacs, it forms large masses.
Affected birds show severe weight loss, depression and intolerance to exercise.
Labored breathing may or may not occur. These symptoms are usually the result of fibrous clots caused by the fungus in the blood supply to and from the lungs. Aspergillosis causes the destruction of nearby affected tissue that could include bone or beak. Aspergillosis that infects the nasal cavity typically involves dry lesions and destructive swelling in one nostril. If Aspergillus is found without other related symptoms it may not be an indication of this condition, because these spores are found normally in the environment.