Flight Formation: The Vs Have It!

Reading Writing Selection

Reading and Writing Connections

Photo: Operation Migration
Did you know that migrating whooping cranes in the wild hardly have to flap at all on a journey that carries them thousands of miles? Every autumn they make their way from Wood Buffalo National Park in Canada all the way down to the Aransas National Wildlife Refuge in Texas, and all the way back again the following spring, by riding thermals. While these wild whooping cranes are migrating, they stay in small family units typically consisting of two parents and one full-grown chick.

The captive-bred whooping cranes make their journey in a very different way. The young birds in the new reintroduced Eastern flock will be flying with an ultralight plane instead of with adult cranes leading the way. The birds will have to flap on the entire journey between Necedah National Wildlife Refuge in Wisconsin and Chassahowitzka National Wildlife Refuge in Florida. That will be a lot of work! How will they accomplish this? The answer lies in how they line up in their flight formation behind the ultralight.

Wake . . . Up!
Eddies of air trail behind each crane's wings. Each bird gets some lift by staying in the current of the previous bird's outer wing. The first bird gets the biggest lift, because the eddies behind the ultralight are more powerful.
An ultralight aircraft can't ride thermals, but it CAN give the cranes following it some help. As the tiny aircraft cuts through the air, eddies of rising air follow in its wake. Just as a motorboat traveling through water leaves a wake in the water, the ultralight leaves this wake in the air. The rising eddy at the tip of the ultralight's wing helps hold the first bird up. This bird's wings produce another rising eddy (though not nearly as big as the one produced by the ultralight). The outer wing of each bird produces eddies that the following bird can "ride on" to help maintain altitude. The bird closest to the ultralight gets the biggest lift. The bird closest to the wing of the ultralight hardly has to flap at all. But the other birds do — and the amount of flapping increases with their distance from the wing. That's why the birds furthest from the plane get tired first, but even these birds get a little advantage from flying in the plane's wake. By looking at the birds' formation, we can see exactly where the wake of the plane is.

Try This!
To see what a wake looks like, fill a bowl or sink with water. Slowly run your finger through it and watch the motion of the water. The motion is similar to the wake made by a boat in water. Does the wake get larger or smaller as you go faster?

Flying With Ultralights: Working in Pairs
Even the first crane gets tired much more quickly than it would if it could ride thermals. So the ultralight-led migrations fly shorter distances than cranes in the wild that are following their parents. The ultralights and cranes take off early in the morning when wind is normally calm. The flight crew considers the weather forecast to decide how far they are going to fly that day; the ground crew must set up where the cranes are going to land. As the morning progresses, headwinds may build, making it harder for the cranes to fly. The second ultralight following in back (the" chase" plane) can help lead any birds that get too tired to follow the lead plane, so all the birds will make it to the day's destination. In the wild, young cranes following their parents would leave later in the day when thermals were well-developed.

Try This! Discussion
Compare Giant Canada Geese with Sandhill Cranes and Whooping Cranes by studying the chart below. Then answer these questions:
  1. Why do you think wild cranes fly on thermals but wild geese do not?
  2. Why do you think geese follow landmarks but cranes do not?
  3. Why do you think geese fly in 'V' formation but cranes do not?
  4. Why can geese following an ultralight cover more miles per day than cranes can?

  Giant Canada Goose Sandhill Crane Whooping Crane
Weight 11 - 15 pounds 6 - 14 pounds 14 - 17 pounds
Body Length 48 inches 34 - 48 inches 49 - 56 inches
Wing span 6 feet 6 - 7 feet 6.5 - 7.5 feet
Wing shape pointed round round
Flight speed 40 - 55 mph 25 - 35 mph 35 - 45 mph
Wing beats fast slow slow
Ride on thermals? no yes yes
Follow landmarks? yes no no

National Science Education Standards

  • Use data to conduct a reasonable explanation.