Possible Clues:

• Tried hard to be as good as someone
• Imitated
• 'Make a date with a mule, but not originally (8)'
• Acted like
• Tried to be like
• Took after
• How the mule got broken over a boy and reproduced
• Rivalled
• The bird might be dead with 500 more, but not originally
• Tried to equal or copy