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Whooping Crane Migration Update: April 1, 1999

Today's Report Includes:

The Journey North Begins!

Dear Students,
The whooping crane migration is underway! Six adult pairs and one family group (2 adults with their chick) have headed north. I did an aerial census flight on March 25 and found only 164 out of the flock total of 183.

Saying Good bye to the Neighbors?
All kinds of vocalizations are going on as the cranes depart. I wish I knew what they were saying. We might think they are saying the equivalent of "See you later. I'm off to Canada to nest". But in reality, the loud whoops are presumably more related to their territorial and dominance behaviors.

When a territorial pair departs, this often influences their neighbors to leave shortly afterwards. Departures are never randomly spread across the wintering grounds. Instead they occur in a clumped pattern.

This year for example, all of the documented migrating pairs so far have departed from the Aransas National Wildlife Refuge--not the nearby wetlands. The Lobstick pair, (named after the creek where they build their nest up north), started the migration approximately March 21. They are usually one of the first pairs to arrive in Wood Buffalo National Park, 2,600 miles to the north in the Northwest Territories of Canada. The Pipeline Flats pair, the Middle Pond pair, and the Middle Sundown Bay family, have all departed from neighboring territories at Aransas. In contrast, no adult pairs or families have migrated from areas next to the Aransas Refuge, where whooping cranes also spend the winter. No birds have left from San Jose, Matagorda, or Welder Flats. This chart shows where birds were as of my March 25 flight:

How Many Cranes Are
Still on the Wintering Grounds?




San Jose




# Adults







# Young








As of March 25


Challenge Question #4
"When do young whooping cranes leave their parents for the first time? And, since migration is so dangerous, why do you think the juveniles migrate 2,600 miles to the north if they're not going to nest?"

(To respond to this question, please follow the instructions below.)

I'll fly once a week over the marsh throughout April to monitor departures. A majority of the cranes will leave between the 7-14 of April. A few of the younger, non-breeding cranes may still be here at the end of April before they fly north in early May. You can use data from the chart above to graph the range of departure dates this year. Make a line graph showing the number of adults, young and total cranes still on the wintering grounds each week.

This departure schedule may vary by about a week from year to year, but is remarkably consistent. That is because the departures are based on hormonal changes the birds are undergoing that are related to the longer days in the spring.

Even with so many cranes leaving within a short time period, they do not travel together. They leave in small groups of 2 or 3 cranes, at staggered starting times. Sometimes, two such units will join forces. So possibly 5 cranes, or occasionally a few more, may be flying together--but not the entire flock.

The 15 whooping cranes that have started the migration are bound to encounter some spring snow storms. Fortunately, they can tolerate cold weather very well and will simply wait until the storm is over to resume their journey. Lets hope every crane has a safe trip. With only 183 total in the wild flock, it is very important that nearly all of them survive the migration.

Until next week,

Tom Stehn
Whooping Crane Cooordinator
US Fish and Wildlife Service

Keep Your Eyes on the Skies
Watch the weather conditions along the Texas Gulf Coast this week, because the whooping cranes should be leaving any day! After the migration begins, plan to keep a close eye on the skies of the Central Plains. During the month of April, whooping crane migration updates will be posted every Thursday, so you can follow their progress closely. You'll need these daily weather maps to analyze the weather:

A Good Day to Fly?
According to Stehn, cranes usually depart when high pressure systems brings sunshine to Texas and winds from the south or east. Thermals and strong southeast winds provide ideal migration conditions. In fact, all along their migration path, the whoopers wait for high pressure and favorable winds to continue their migration.

The least favorable conditions for crane migration are low pressure systems with north winds. Low pressure systems are associated with storms. When the migrating whoopers encounter these storms with their north winds, the birds will quickly find a place to land. They'll wait for several days until the north winds rotate back around to the south.

During these storms, the whoopers will make short daily flights out to grain fields to feed, returning to wetlands where they will spend the night. It is during these short low altitude flights where they might collide with power lines and be killed, especially during rain or snow storms when the power lines are not very visible.

How Do They Know When it's Time to Go?
One of the most important abilities of any migratory animal is its ability to tell time. An animal's very survival depends on being at the right place at the right time. The hormonal changes Tom Stehn mentions are controlled by invisible "biological" clocks that work within the cranes' bodies.

Researchers have learned that people have over 100 "biological" clocks which control the rhythms of our lives. These clocks control sleep, hunger and energy cycles in interesting ways. In the lesson below, explore the concept of time--and learn about your own biological clocks. Then consider the importance of biological clocks to migratory species.

Challenge Question #5
"What if an animal lost track of time? Choose one Journey North migratory animal and write a story telling what would happen. Consider all the activities the animal must do on time--according to daily and yearly schedules. Then send us your story!"

How to Respond to Today's Challenge Question
1. Address an e-mail message to: jn-challenge-crane@learner.org
2. In the Subject Line of your message write: Challenge Question #4 (OR #5).
3. In the body of your message, answer the question.

The Next Whooping Crane Migration Update Will be Posted on April 8, 1999

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