Whooping Crane Migration Update: March 4, 1999
Today's Report Includes:
Overview of the Crane's Journey North
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
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).
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:
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!
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: firstname.lastname@example.org
The Next Whooping Crane Migration Update Will be Posted on March 18, 1999
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