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Tom Stehn's Report: Frustration
Feb. 13, 2009
Meet Tom Stehn
Whooping Crane Coordinator, U.S. Fish and Wildlife Service

As you read Tom's report this week . . .
  1. How many cranes were at Aransas NWR when Tom first counted them in 1982? How many are there today?
  2. What is unusual about this winter at Aransas?
  3. What do Whooping cranes need in good winter habitat? Why?

 

Dear Journey North,

People often ask: What is the highest number of cranes anyone has ever counted at Aransas? I did my first count in fall 1982. Only 73 whooping cranes were present that winter. The good news is that the flock has grown. This week I flew over the refuge to count cranes for the seventh time this season and my best estimate for the peak population this winter is 232 adults + 38 young= 270. "Best estimates" are a part of science, but I don't have as much faith in its accuracy as I do in most years. Here's why:

This has been my most frustrating winter at Aransas. This week's flight indicates that so far 11 Whooping cranes have died this winter at Aransas. That is a loss of 4.1% of the wintering population (11 out of 270). We have just one or ZERO crane deaths in normal winters. The all-time worst winter on record was 1990 when 11 out of 146 Whooping cranes died at Aransas. In the last 20 years, the current winter ranks as the third worst in terms of mortality (deaths). Why is this happening?
Drought is causing problems in crane habitat. Wolfberries are scarce. Blue crabs are scarce.

Food and fresh water for the cranes is scarce because of the prolonged drought, or period of dryness, in Texas. Crab numbers dropped through November, when hungry cranes were arriving after their 2,700-mile migration from Canada. The crabs had moved out into the deeper bays. Normally cranes will eat the fall wolfberry crop when crabs are few. But the drought made wolfberries scarce too. Not only are their normal marsh foods scarce, but the drought has made the marsh water saltier than cranes can drink. They must spend precious energy to fly farther in search of fresh drinking water. Conditions this extreme have not been recorded at Aransas NWR in the last 26 years. The habitat is not nourishing them after their long migration from Canada. And summer nesting may be affected; research done by Dr. Felipe Chavez-Ramirez in 1994 documented that up to 37% of the Whooping cranes failed to nest following a poor blue crab winter at Aransas NWR.

But take heart. You can look forward to hearing about some of the wonderful crane individuals and pairs I have come to know in my years at Aransas. You'll agree that their stories give us a lot to celebrate.

Tom Stehn
Aransas National Wildlife Refuge
Austwell, Texas

 


 

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