Tom Stehn's Report: Migration Dangers
March 16, 2007
Meet Tom Stehn
Whooping Crane Coordinator, U.S. Fish and Wildlife Service

As you read Tom's report this week . . .
  1. What does Tom mean by a crane's internal clock? When do the cranes normally leave Texas?
  2. What are four of the migration dangers for cranes?
  3. Why is Tom concerned about one whooper family?
  4. Send your questions to Ask the Expert starting March 23.

March 15, 2007

Dear Journey North,
Start your departure log! >>

They're Off! A Question for You
On March 7th, I estimated it was still about 2 weeks until I could realistically expect the first whooping cranes to start their migration from Texas. So wouldn’t you know, on March 8th, two adult cranes with their chick were seen spiraling high in flight and heading north. It was about 10 AM when the cranes were sighted, about the time that cranes start their daily migration. Why do you think they wait until about 9:30 or 10 in the morning to start their migration? The skies today were clear with moderate southeast winds around 15 miles per hour. (Think about that last sentence; it provides clues to answer my question.)

Migration Timing
Not every whooping crane has the same internal clock. Nine of the reintroduced whooping cranes in the eastern migratory population started the migration several days before the family from Aransas started. Usually a few whooping cranes leave Texas during the last week in March, but it is not until April when most small groups of whooping cranes will ruffle their feathers one last time, consume a final sip of brackish water, take a few running steps, pump their 7-1⁄2 foot wings and lift off from the salt marsh. For the next 7 months, all the wetlands that the cranes use will be fresh water — since they are not near any oceans as they migrate through the central U.S. and Canada.

The Hazards Ahead
I want you to think a little about w
hat hazards the cranes face as they migrate north. Many things come to my mind, including snow storms and cold temperatures. We hope the cranes will stay here in Texas long enough so that most of the snow is gone when they migrate north. How do you think the whooping cranes avoid predators whenever they stop during their migration? The largest threat the cranes face is collision with power lines that the cranes simply don’t see and fly into. In fact, such collisions kill more adult whooping cranes than any other factor that we know of. The cranes normally migrate high above such power lines as they rise over a mile high on thermal currents. However, when the cranes come down for the night to look for a safe place to land, they can hit these power lines.
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Oiled Family: A First
One other threat that I had never thought about before surfaced this past fall. A family group of whooping cranes was seen on the Platte River in central Nebraska with darkly stained feathers on their legs and bellies. We think the cranes somehow walked into a pond that had oil on the surface and the birds got oil on their feathers. Oil can cause the feathers to become bedraggled and lose their ability to keep the birds warm. Also, as the cranes try to clean their feathers, they may get sick if they actually end up eating small amounts of the oil.

I have been watching this oiled family group at Aransas this winter. They seemed to be okay, but on my last two searches for them, I wasn't able to find them. I’ll keep looking, and hope to find them in the next couple weeks. The family with the oiled feathers points out how important it is to have clean, unpolluted wetlands scattered throughout the migration corridor so the cranes will have plenty of safe places to stop and rest as they make the 2,400-mile migration across North America to Canada.

Tom Stehn
Whooping Crane Coordinator