What symptom might indicate that a hawk has aspergillosis?

The symptom indicating that a hawk has aspergillosis is a change in its voice. Aspergillosis is a fungal infection caused by the Aspergillus species, which can affect the respiratory system of birds. When a hawk is suffering from respiratory issues due to this infection, it may face difficulties in producing normal vocalizations, leading to a discernible change in its voice.

A change in voice could manifest as hoarseness or a weak call, reflecting the underlying respiratory distress caused by the fungal infection. Other typical symptoms of aspergillosis include difficulty breathing or lethargy, but a change in vocalization is particularly distinctive.

While feather color change and moulting are processes that can occur in birds for various reasons, they are not specific indicators of aspergillosis. Therefore, while changes in voice soundly correlate with respiratory issues, the other options do not have a direct relationship with this particular fungal infection.