Western Flock News

April 10, 2009
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As you read reports from Tom Stehn and Brian Johns this week, look for:
  1. How many wild cranes have begun migration from Texas?
  2. What is the main thing that rules timing of the cranes' departure?
  3. How do the food items eaten by cranes help them in hard times?
  4. Why does Brian Johns compare winter 1993/94 to winter of 2008/09?
  5. What prediction does Brian Johns make about nesting this spring?
Meet Tom Stehn
Whooping Crane Coordinator, U.S. Fish and Wildlife Service

Dear Journey North,
I was quite surprised when I did a census flight of the whooping cranes on April 7th and found out a little over half the flock has started the migration. Among them were the family group I call Al and Diane and their twins.That's good news!

This year the migration may be slightly on the early side, but well within what we would consider to be normal.

  • What dangers do you think the cranes would face if they migrated too early?

The poor nutritional state of the birds due to the winter food shortage here at Aransas has not held up the migration. (I did not expect it to.) Migration behavior seems so timed to the length of the days that it never seems to vary by more than about one week from year to year. As spring advances, the lengthening days serves as a trigger to initiate the migration. I have no idea how the birds measure or "know" that the days are getting longer. The birds just somehow get the urge to migrate.

It has been such a struggle for the whooping cranes this winter due to the lack of blue crabs. You can see in the picture how disheveled the plumage looks, and how the feathers (which are snow white) have a touch of gray on them. Photo USFWS

Hopefully, the cranes will find much more food to eat when they reach Canada as they forage on minnows, berries and insects, a diet found in the freshwater marshes of Canada that is so different from the salt marshes here on the Texas coast. Whooping cranes are omnivorous, meaning they eat just about anything (animals and plants). That behavior will help them survive through these tough times.

Tom Stehn
Aransas National Wildlife Refuge
Austwell, Texas

Meet Brian Johns
biologist, Canadian Wildlife Service

Dear Journey North,
After the dry winter with food shortages on the wintering grounds the cranes can look forward to more normal conditions when they complete their spring migration. Habitat conditions on the breeding grounds in Wood Buffalo National Park appear to be near normal. Snow is in the process of melting. Today's high is +7C but the temperatures are still below freezing at night.

During the winter of 1993/94, the cranes went through an experience on the Texas wintering grounds similar to this year's. Losses of adults were higher than normal, and the cranes were not in peak breeding condition by spring because of food shortages during the winter. That year migration was erratic, with some birds leaving Aransas earlier than normal and other birds lingering longer than they normally would. Breeding adults were still in migration when they should have been incubating eggs in Canada. Once migration was complete, several of the pairs did not nest— likely because they were in poor condition. This resulted in a 35 percent reduction in the number of nests from the previous year.

With this winter's similar conditions, it is likely that we will see a reduction in the number of nests this summer. Our surveys will begin in mid May, when the pairs are nesting, and we should know at that time if there will be any reduction in nesting attempts this year.

Brian Johns
Canadian Wildlife Service
Saskatoon, SK
Wood Buffalo National Park