Possible Clues:

• 0 Water birds
• Delta fliers?
• Some migratory birds
• Fliers in formation
• Gosh! South-Eastern birds
• With 50-Across, it's represented by 15 squares in an appropriate arrangement in this puzzle
• Silly ones in a gaggle
• Turning say round notice, they'd want a gander
• Winter migrators
• Foolish folks