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Tom Stehn Reports from Aransas: March 26, 2003
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Tom Stehn and Survey Plane |
The whooping crane migration has started! My census flight today (March 26) indicated that up to 14 of the 184 whooping cranes in Texas had started the migration. They must have departed on March 24-25, the only days with favorable tail winds since my last flight on March 19th.
If you think of the cranes with their magnificent 7.5- foot wing spans, why do you think they wait for tail winds to migrate? Maybe if someone in your class has really long legs, think of them trying to run from the US to Canada. Wouldn't that person wait for a ride or buy a bus ticket to get there faster? The cranes do the same thing; they wait for the best conditions to make the trip easier, and tail winds sure help. But they can't wait too long. They need to get up to Canada and nest, lay eggs, raise young, and teach the young to fly-- all before October blizzards hit and turn northern Canada back into a frozen ice cream cone. Can you think of what other weather condition the cranes need that is equally as important as tail winds for the migration?
I had quite a workout last week counting blue crabs in the marsh. The most I found were 56 in about a one mile hike through the marsh. That is about one day's food supply for one crane and explains why they need long legs to cover lots of ground to find plenty of food. Blue crabs are their favorite food and are needed by the thousands for whooping cranes to stay healthy. I found crabs just about everywhere in the marsh. Thus, with lots of food this winter, the cranes should be in excellent shape to migrate north and nest.
Want to hear what I did while doing the crab counts that was really stupid? At one point, I stepped on something very hard, but couldn't see what it was because of the mud I stirred up as I walked. I figured it was a bottle and reached down to pick it up, figured I'd be rewarded by cleaning up the environment. As I pulled my hand from the water, a very large crab was attached to my thumb, and within a fraction of a second, its claw was pinching my thumb. I had stepped on the hard shell of the crab. I immediately jerked my hand back and the crab detached its claw and got about a 20-foot flight through the air. This was definitely a new experience for both myself and the free-falling crab. You won't need to remind me not to stick my hand down into the marsh again unless the water
is clear.
One last item: the question I asked you last week. What factor is it that is most important in determining when the cranes migrate? The answer is the amount of daylight. As the days get longer in the spring, this triggers physical changes in cranes. Scientists can measure these changes by the amount of weight gain and by analyzing hormones found in the blood. When the days reach the right length and the birds are physically ready, off they go. They reach this physical condition at different times. Thus, migration departures are spread out over a period of as many as 6 weeks. What a determination they have to fly 2,400 miles to their nesting grounds in Canada.
See you next week.
Tom Stehn, Whooping Crane Coordinator
U.S. Fish and Wildlife Service
Aransas NWR
P.O. Box 100
Austwell, TX 77950
Copyright 2003 Journey North. All Rights Reserved.
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