Possible Clues:

• Intruder bird in the nest
• Is the brown bird daft?
• Foolish - bird
• Crackpot bird?
• Bird that invades another's nest
• Bats counting as bird? Yes and no
• In the nest, it's an intruder
• Unwelcome bird in the nest
• No home bird, this slightly mad type
• Lords and ladies obliged to have pint with this fool