Clue: Nocturnal birds, alias parrot's head, found in Greek island (7)
Answer: KAKAPOS
Explanation: Definition: Nocturnal birds
**AKA** (also known as, "alias") + **P**(arrot) [*'s head*], *found in* **KOS** ("Greek island") 
 
 
*Kakapos are rare nocturnal parrots from New Zealand.