Do Whooping Cranes Migrate in Small Groups and Leave at Different Times?
The crane departures from the wintering grounds take place over a period of around 3-5 weeks. Many of the cranes leave at different times. Whooping cranes travel in small groups, often in groups of 5 or fewer. Single cranes sometimes even make the migration by themselves.
Migrating in small groups and leaving at different times gives an advantage to the flock in case they encounter hazards on the migration. For example, they could encounter severe blizzards and actually be killed by freezing sleet. Or they could stop in a wetland where they might be exposed to a disease outbreak. But the largest source of crane mortality is collision with power lines that the birds don’t see when flying, especially late in the day or early in the morning when making short flights from their stopover locations in seach of food
With cranes leaving at different times and stopping at different places, not all the cranes are exposed to the same hazards. That ensures that some cranes will survive and means a real advantage for the flock to migrate in small groups at different times.
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