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Tom Stehn's Report: Going. . .going. . .
April 8, 2011
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Tom Stehn looks for Whoopers at Aransas NWR

As you read Tom's report this week . . .

  1. How many cranes remain at Aransas this week?
  2. How many radio-banded cranes are in this flock now?
  3. What new things did you learn about Whooping crane territories?
  4. What clues do cranes show as they are about to start migration?
Image: Klaus Nigge

Dear Journey North,

On April 6, refuge staff saw 3 cranes at the refuge boat ramp, and Tour Boat Captain Tommy Moore had 2 on Ayres Island; these were the only cranes he saw on his tour. Reports indicate Nebraska was "chock full" of cranes April 1-4. At least 15 Whooping cranes arrived on the Platte on April 2. On the morning of April 8th, all of the radioed birds were gone from Aransas, taking advantage of the southerly winds. Right now the 11 radioed birds range from N Texas to near Bismark ND. It looks like the migration is well underway—perhaps a week early—and the cranes may be in Canada soon depending on snow and water conditions in the northern U.S.

A Special Pair Starts Migration
The territorial pair at Mustang Lake in front of the refuge observation tower apparently started the migration the morning of April 6th. This winter, the pair consistently stayed on their territory and were in sight daily to over 40,000 visitors from all over the world that came to see them. Those visitors had climbed a 40-foot tall tower to gaze out over the salt marsh to look for the tall white birds stalking blue crabs and eating wolfberries. The territory of the Mustang Lake pair is nearly a square mile in size; the pair defends that area and protects the food supply it contains from all other whooping cranes. That is the purpose of establishing and defending a winter territory: It provides the food a pair needs to sustain themselves throughout the winter.

Territories in Two Seasons
Whooping cranes are unusual in that they defend territories both in the summer and in winter. Most birds only have summer territories. What is the main difference between a summer territory and winter territory for a Whooping crane? Think about what Whooping cranes do every summer.

Watch for Clues for Departure
Most of the whoopers should be departing by April 10. They normally start migration flights between 9:30 and 10:30 (but could be as late as 11:00) because they wait for the thermals to build up and of course need tailwinds. Sunshine is preferred.

If you see them between 9 and 9:30, you may start getting clues of the impending takeoff. They will look more "antsy" than usual, with the male showing much more alert behavior, walking around, and even occasionally turning his head sideways and gazing at the sky. Finally, a pair will take a final drink of water, group up, and take off. You never know what day it might be. But the adult pairs should be leaving soon, while the subadults could stay through most of April.

Tom Stehn, Whooping Crane Coordinator
Aransas National Wildlife Refuge
Austwell, Texas

 

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