Possible Clues:

• The cuckoo has but is not
• What the cuckoo's got isn't
• 'This isn't what the cuckoo has (3,3)'
• What the cuckoo has just isn't
• 'What the cuckoo lacks just isn't (3,3)'
• Is not what the cuckoo has
• It is like the cuckoo though it is not
• Was the cuckoo extinct in Rome?
• No birds at home there
• This might make the cuckoo extinct