Related Clues:

• See 18-Across
• Mass movement
• Birds' semiannual flight
• Periodic passage of animals from one place to another
• Periodic passage of animals
• Periodic movement of groups of animals
• The movement of people or animals from one locality to another
• Russian aircraft with share of international travel?
• Grit Naomi displayed in returning with Ruth
• Restriction on Soviet aircraft moving elsewhere
• Annual movement from one place to another
• Dutch instrumental duo who notched a UK No one in nineteen ninety four
• Aircraft helping movement of people
• Wandering fighter given an allowance
• Jet helping movement of people