March 15, 1996
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, as shown in the chart below.
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 is melting from the marshes.
Tom Stehn, Refuge Bilogist at Aransas National Wildlife Refuge in Austwell, Texas will provide updates this spring as the cranes begin their migration. His first report is attached below.
Whooping cranes mate for life, and we'll pay special attention this spring to the "Nyarling pair", the most popular crane couple. This is the pair people are most likely to see when they visit the whoopers' winter home in Texas. They're named after the Nyarling River which flows beside their nest in Wood Buffalo National Park.
Can you find Aransas National Wildlife Refuge on a map, near Austwell, Texas? Also try to find the Nyarling River in Wood Buffalo National Park. (The Park is located on the border of Alberta and the Northwest Territories.)
A network of people along the whoopers' migratory path watches over their journey each spring and will report to us periodically.
Year Population Size
1940 22
1950 34
1960 33
1970 56
1980 76
1990 146
1991 132
1992 136
1993 143
1994 133
1995 158
(This represents the peak count for winter, always in December.)
To: Journey North
From: Tom Stehn
Aransas National Wildlife Refuge
Austwell, Texas
Dear Journey North Students
March 7, 1996
It has been a phenomenal year for the whooping crane. A record 158 cranes arrived at Aransas this winter. Numbers went up 25 cranes from last spring, the largest one-year increase ever. Only one other time (in 1987) had the population increased by more than 20 birds in one year. Nobody had expected this kind of growth.
Last winter, the marshes were full of blue crab, the favorite food of the whoopers. This allowed the birds to survive the winter and complete the spring, 1995 migration in good heath. Despite poor water conditions up in Wood Buffalo National Park where they nest (in the Northwest Territories of Canada, about 200 miles south of the arctic circle), a record number of nesting pairs (49) produced 45 chicks. A record 28 chicks survived the summer and fall and made it to Aransas. The previous high for chicks at Aransas was 25 in 1987.
The 158 I have counted this winter represent a loss of only 3 cranes since spring of 1995 ( 133 in spring + 28 chicks - 3 deaths = 158). Since about a dozen whoopers have been dying every year, the loss of only 3, combined with the record number of chicks, led to the record number of cranes here this winter. Blue crabs have been plentiful again this winter and all 158 cranes survived.
The first of the whoopers should be leaving soon, sometime before the end of March. However, because over the years, whoopers that have left too early may not survive, most of the whoopers will wait until the first two weeks in April to head north. The breeding pairs are always the first cranes to leave since they have to get to Canada by the end of April to nest. Their timing is magnificent since they ususally get to Wood Buffalo just after the ice has melted. Within 1-2 weeks after the migration, the pairs have built nests and are taking turns sitting on their two eggs. Especially interesting this winter was a study of bobcats here at Aransas.We radio-collared 34 bobcats (it took us 1 full year using 50 traps every night to catch that many different cats). Since bobcats occasionally kill whooping cranes, we were very interested to see how often bobcats go out into the marshes where the whoopers spend the winter. Occasionally, bobcats got close to whoopers, but weren't able to kill any since all the whoopers were heathy, alert, and primarily stayed in ponds where the cats can't sneak up on them. We like having bobcats in Aransas. They rarely can ever catch a healthy whooper. In fact, we have seen an adult whooping crane chasing off a bobcat. However, a cat may remove a sick whooper from the population. Why do you think it is okay if a bobcat would catch a sick whooping crane?
The Nyarling pair of cranes has been very cooperative all winter, staying in their territory where refuge visitors view them from a tall observation tower. Occasionally, a neighboring family group would come and dig clams on the edge of the Nyarling pair's territory, but Nyarling would not let them intrude. Why is this beneficial for cranes to have territories which they keep other cranes out of?
I'll be flying once a week this spring to look at the cranes and learn when pairs start the migration. Let us hope they have another great year.
Sincerely,
Tom Stehn
Refuge Biologist
Aransas National Wildlife Refuge
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