Possible Clues:

• Birds with no get-up
• Large birds of the pampas
• Flightless birds share a dog's dinner
• When rook soars, catches birds that can’t
• Birds harassed hares
• More than one bird rises up, it's said?
• Grounded birds of 14-Across
• Some very large flightless birds
• Ostriches’ South American cousins
• Hears about birds unable to fly