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!
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.
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! Demonstration
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?
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
Compare Giant Canada Geese with Sandhill Cranes and Whooping
Cranes by studying the chart below. Then answer these questions:
- Why do
you think wild cranes fly on thermals but wild geese do not?
- Why do
you think geese follow landmarks but cranes do not?
- Why do
you think geese fly in 'V' formation but cranes do not?
- Why can
geese following an ultralight cover more miles per day than cranes can?
- 15 pounds
- 14 pounds
- 17 pounds
- 48 inches
- 56 inches
- 7 feet
- 7.5 feet
- 55 mph
- 35 mph
- 45 mph
Science Education Standards
- Use data
to conduct a reasonable explanation.