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Tom Stehn's Report: Troubled Times
March 20, 2009
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As you read Tom's report this week, look for answers:
  1. What did Tom's latest census flight reveal?
  2. How does the current winter compare with other winters for crane losses?
  3. What signs of a bad winter diet do the birds show in their appearance?
  4. What are the pros and cons of supplemental feeding for birds who, in better times, can find their own natural food? How are they carefully monitoring as many of the "cons" as possible?
  5. When does Tom expect migration to begin?
Meet Tom Stehn
Whooping Crane Coordinator, U.S. Fish and Wildlife Service

Dear Journey North,

Juvenile at Feeding Station
Photo USFWS

My most recent aerial Whooping Crane Census flight census took place on March 15th. Just short of 4 hours, we stopped the flight due to overcast skies and light rain, leaving parts of the crane range not flown. The estimated peak number of Whooping cranes in the 2009 winter flock was 270 (232 adults and 38 juveniles). This flight provided evidence of 3 more mortalities since my last census. An estimated 21 whooping cranes have died this winter at Aransas. The current flock totals 249 Whooping cranes (226 adults and 23 juveniles). This brings the total winter mortality to an estimated 21 birds: 6 adults and 15 chicks, or a loss of 7.8% of last fall’s record sized flock of 270.

Worst Winter for Crane Losses
Out of the last 20 years, the current winter ranks as the worst in terms of mortality. It's more than in 1990 when 7.5% of the Whooping cranes (11 out of 146) died at Aransas. The 21 deaths this winter can be added to the 34 Whooping cranes that left Aransas in the spring of 2008 and failed to return in the fall. Thus, 55 Whooping cranes have died in the last 12 months, or 20.7% of the flock of 266 present at Aransas in the spring, 2008.

Problems With the Food Supply
Blue crabs are still scarce due to the record-setting drought. These are the worst conditions I have ever observed for the cranes at Aransas, with some birds looking thin and with disheveled plumage. I wish I had better news to report. Meanwhile, the refuge is continuing supplemental feeding with corn. Remote motion-activated cameras let us monitor how many cranes are feeding at all refuge feeders.

Supplemental feeding has its pros and cons. See what you think. We are carefully monitoring as many of the "cons" as we can, putting feeders in places with minimal risk of predation, making sure cranes continue to eat natural foods, making sure aggressive interactions aren't occurring, making sure the corn stays dry, moving the feeders as needed to prevent diseases from building up in the soil. So far we don't see much in the way of negative aspects of providing supplemental food. However, only a limited number of cranes are using the feeders, and we currently are not measuring how much corn the cranes may be eating, making it hard to measure the impact of the feeders.

Will Migration Be Affected?
I have no idea how the poor habitat conditions due to the record-setting drought may affect the timing of the migration, which seems to vary by only about one week from year to year. A few Whooping cranes start leaving Aransas the last week in March, with the majority of the cranes departing the first two weeks in April. The last of the breeding pairs are usually all gone by April 21st, while a few sub-adults occasionally stay into May. One juvenile Whooping crane was confirmed on the Platte River in Nebraska on February 20th. We think this is the juvenile that over-wintered in Oklahoma and likely moved north to the Platte with Sandhill cranes.

My next census flight is scheduled for the week of April 6th. I should have some good migration news to report!

Tom Stehn
Aransas National Wildlife Refuge
Austwell, Texas


 

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