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Whooping Crane Migration Update: March 4, 1999

Today's Report Includes:

Overview of the Crane's Journey North

Migration Route
Map by Claudia Fonkert
Macalester College

The whooping crane is an endangered species with a success story to tell. Their population hit an all time low in 1940 when there were only 22 cranes left in the wild. Their numbers have been steadily building, year-by-year, to a total of 183 today.

Each spring the entire flock of wild whooping cranes takes the annual 2,700 mile journey from their wintering grounds in Texas to their nesting grounds in northern Canada. They usually arrive in late April or early May, just as the ice and snow are melting from the marshes.

Also each spring, before the cranes begin their journey, Tom Stehn, Whooping Crane Coordinator for the U.S. Fish and Wildlife Service provides updates for us from the cranes' winter home on the Texas Gulf Coast. He filed his first report today. Once the migration is underway in April, weekly weather reports and migration news will be shared once again this
year by Wally Jobman. Wally is based at the U.S. Fish and Wildlife Service office in Grand Island, NE. Finally, from the far north, Canadian biologist Brian Johns, of the Canadian Wildlife Service, will share the excitement when the cranes arrive once again on their ancient nesting grounds.

We hope you enjoy traveling with the whooping cranes this spring!

Update from the Crane's Winter Headquarters in Texas
Juvenile whooping cranes are tawny colored, in contrast to the full white of the adult.

Dear Journey North:

Greetings from the Texas Gulf Coast where the whooping cranes are preparing to start their spring migration. Hormonal changes in the cranes are now allowing them to gain weight and build up the fat reserves that they will need for the long migration. The entire population will travel to Wood Buffalo National Park in the Northwest Territories of Canada (60 N, -114 W).

The first whooping cranes normally start the migration about mid-March. A few could leave a little before that, but most of the population leaves during the first half of April. I'll be flying in a small airplane once a week all spring to record the number of whooping cranes that start the migration each week. I'll let you know how the count is going. Despite warm spring weather here, the whoopers "know" it is too early to start their journey since it is still frozen up north.

Blue Crabs Can Mean More Cranes
Conditions for the whoopers at Aransas were excellent this winter. Blue crabs are the whoopers' favorite food item--and important to help them built up enough energy reserves to have a successful nesting season. Blue crab counts in November and December were extremely abundant and, although declined in number, remained available into February. In 1994, when blue crabs had been scarce, about half of the whoopers failed to nest that summer! We think this was because they weren't in good enough condition. (See impact on 1994 population size, chart below.)

Population Climbs by Only One Crane
The past year has been a struggle for the whooping cranes--and disappointing for us. The flock managed to INCREASE their numbers, but by only ONE crane. The flock now consists of 183 birds: 100 adults, 65 subadults, and 18 young. This is a record number, but average mortality apparently kept flock size below the 190+ cranes we hoped for. Production of more than 20 young, and mortality of less than 10 adult/subadult birds over the summer, is needed for the population to show a big increase.

Below is a brief chronology of their year. If you read carefully, you should be able to answer these important questions--the kind I'm concerned with every day in my work:

Challenge Question # 1:
  • How many chicks were produced this summer? How many fledged?
  • How may young completed their fall migration?
  • What % mortality occurred of the young post-fledging? Was this average?
  • What percent of the adult/subadult population failed to arrive this winter? Was this average?

To respond to this week's Challenge Question, see below

Refuge Biologist
Tom Stehn

Summer, 1998 Wood Buffalo National Park: In Canada this summer, 49 nesting pairs produced 48 chicks. This included 12 pairs with twin young-- but none of the sets of twins young survived. (Only ONCE in 33 years have twins reached the wintering grounds, when a set of twins arrived safely in 1997. This hadn't happened since 1964! Read about the successful twins here!) In mid-August, 1998, as they began flying lessons at about 10 weeks of age, only 24 chicks were still alive.

Fall Migration, 1998, Canada to Texas: Sixteen adult/subadult cranes (9% of the population) failed to arrive at Aransas. Another indication of mortality during the fall migration was that, of the 24 juveniles fledged in August in Wood Buffalo, only 18 made it to Aransas by the end of the year. This indicates 25 % mortality of the young post-fledging, an above average figure. If mortality had been less than average, this would cause the population to grow above the peak of 182 last winter. (This compares with 30 chicks that reached Aransas last year.) In some cases, family groups were reported in Saskatchewan but failed to arrive at Aransas with their juvenile.

Spring Migration, 1999: Keep a close eye on weather conditions along the Texas Gulf Coast--and we'll watch for the migration of 1999 to begin!

Tom Stehn Whooping Crane Cooordinator USFWS

Suggestions for Analyzing Whooping Crane Population Data
This link provides population figures for the entire flock of wild whooping cranes! Using the data from 1940 to the present, you can make 3 graphs to help you analyze the population comeback.

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 #1
3. In the body of your message, answer the question.

The Next Whooping Crane Migration Update Will be Posted on March 18, 1999

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