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Tom Stehn's Report: Good News, Exciting Day
March 28, 2008
Meet Tom Stehn
Whooping Crane Coordinator, U.S. Fish and Wildlife Service

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

  1. What does Tom expect the Lobstick male will do this summer?
  2. Why are blue crabs important in cranes' winter diet?
  3. What clues told Tom the birds were starting migration?
  4. What kind of weather do cranes choose for migration? Why is this a smart choice?

Dear Journey North,

I have good news this week about the Lobstick male you met in my last report. Earlier in the winter, this crane was having difficulty flying. I was very worried. For about two months, he seemed to limit the amount of flying he did. Sometimes he avoided flying altogether. When intruding whooping cranes entered the Lobstick territory, Daddy Lobstick would make a short flight towards the intruders, but then walk several hundred yards to reach them and chase them off. Those long walks were not normal behavior. One time his mate and their juvenile flew off towards the uplands; the Lobstick male stayed behind, calling forlornly. Something was definitely wrong with him.

His flight feathers looked fine and he was feeding normally, but had he torn a flight muscle or suffered a shoulder injury? I was very worried that perhaps Lobstick’s old age was catching up with him. After all, he is nearly 30, and the oldest known-age crane in the flock. However, after a couple months, he began to resume his flying. He started flying farther and higher off the ground — good signs that things were back to normal. I think he will migrate normally and next be observed in Canada tending a nest and raising young (and celebrating his 30th birthday).

Start of the Migration
March 25th was an exciting day for me. I had hiked the marsh for two hours, counting blue crabs. We do this to assess the amount of food available to the cranes. The blue crab supply can be an indicator of how well the cranes will do in the upcoming nesting season.

As I was walking back to my truck, I saw 3 cranes in flight low over the edge of the marsh and heading north. Were they heading for a pond to get a drink of fresh water since the marsh is currently very salty? But the cranes started circling and continued flapping — a sign they were working hard to gain altitude. Higher and higher they got, and soon they passed by the pond where they sometimes drink. As they 3 cranes got father away, I memorized the shape of a cloud that was behind them as they became harder and harder to see. It was clearly the start of a migration flight. What a thrilling sight to see.

Whooping Cranes Travel in Small Groups
A refuge volunteer who was helping me with the crab count saw two other cranes that were also starting the migration at the same time. The crane groups of 3 birds and 2 birds did not join together. Each group will migrate independently. Can you think of reasons why it would be an advantage for Whooping Cranes to fly in small groups? Are there disadvantages?

The Right Weather
As I watched the cranes start the migration, I saw how hard they were working to gain altitude as they continually flapped. I thought of how far they must fly to reach the nesting grounds in Canada, an amazing 2,400 miles. How will they have the strength to go all that way? The key to answering that question is the weather.

Thermals Help Cranes Save Energy
As I watched them depart, the cranes had selected a day with tail winds of about 20 miles per hour to help push them north. It was a warm day with sunshine and very few clouds in the sky. Soon the cranes would be catching thermal currents and soaring on their 7-and- one-half-foot wing spans. Once the cranes find the thermal currents, they don’t have to keep flapping. They rise on the thermals to more than one mile high. Then they glide downwards at up to 60 miles per hour to aid their migration. This helps them save energy. I sure hope they were able to eat enough blue crabs before the last few weeks before they left to given them the strength they need to fly for the next 3 weeks or so to reach Canada.

The five cranes seen migrating were the first cranes that we knew of to migrate this spring. The journey is underway.


Tom Stehn
Aransas National Wildlife Refuge

 

P.S. Last time I promised to write a little about why the growth rate for Whooping Cranes is so low, and I asked you to do the same. You can read my answer next week.

 

 

 

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