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Tom Stehn's Report: Migration Picks Up
April 2, 2010
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As you read Tom's report this week . . .
  1. What weather conditions are the best for migration?
  2. What two families departed this week on migration? What is special about them?
  3. What new things did you discover about Whooping crane migration?

LATE NEWS : As of April 2, crane numbers were cut in half. "A notable number of cranes left Aransas the last 3 days in March and 1st day in April. It seems like the migration is at least a week ahead of average this spring."

 Photo Howard Murph

Dear Journey North,
A cold front brought northwest winds to the area on March 28 that would have halted all bird migration. It took a full day on the 29th for the winds to swing around from the opposite direction and strengthen. As soon as the winds calmed down and shifted direction on that morning, the cranes you know as
"Al and Diane," the resident pair on the Lamar Unit of the Aransas NWR and also known as the "Johnson" cranes, apparently started their migration. This is in keeping with their normal pattern of starting the migration around April 1st!

On March 30 the conditions were perfect for migration: clear skies with sunshine providing thermal currents, and strong southeast winds (tail winds) at 15-20 mph. At least three cranes took full advantage and headed north at 10:45 a.m. when refuge volunteers saw them in flight over Jones Lake on the Aransas National Wildlife Refuge. The three cranes were low, but quickly gained altitude as they spiraled up. We think they might have been the "Boat Ramp" family group. The Boat Ramp female was color-banded as a juvenile in 1987, so we know she is nearly 23 years old.

Other Cranes Getting Ready
The remaining cranes have been busy, doing their daily chores of catching crabs and patrolling their territories to keep all other cranes out and thus protecting their food supply. Many will be leaving any day now. It will be 6 or 7 months before they return to Aransas. They will migrate 2,400 miles, a trip that takes 3 to 4 weeks. They will travel anywhere from 200 to 400 miles per day. When conditions are favorable (providing thermal currents and tail winds), the cranes will fly about 7 hours per day. If the winds are in their faces, they will stay put. They will look for food to eat near wherever they have found a small pond or wetland to roost in for the night where they are safe from predators. They have to do the what YOU do when you travel: cover a lot of miles, and then look for food and a safe place to sleep.

We're now approaching the peak departure time at Aransas. I expect many whooping cranes to depart in the next two weeks, and nearly all will wait for excellent conditions like we've had the past couple of days. Here we go!

Tom Stehn
Aransas National Wildlife Refuge
Austwell, Texas


 

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