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Tom Stehn's Report: Stragglers?
May 4, 2007
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Meet Tom Stehn
Whooping Crane Coordinator, U.S. Fish and Wildlife Service

As you read Tom's report this week . . .

1. How many cranes remain at Aransas NWR in Texas?

2. What is unusual about two of the cranes still probably at the refuge?

3. What's the latest that a crane has stayed in Texas before migrating?

4. Why doesn't Tom think Whoopers would be successful at nesting if they stayed in Texas?

Dear Journey North,
Click to see the Lobstick crane's swollen neck and head after injury.

As the spring coastal winds have really kicked into gear, I've been waiting patiently to see if the 7 Whooping Cranes counted on my April 19th aerial census have started migration. On April 26th I had reports of 3 cranes still here at Aransas Refuge, and a single crane was sighted April 29th on nearby Matagorda Island. The three cranes at Aransas were not seen on boat trips conducted April 29 and 30, but my guess is that they are still here. One of those three is the Lobstick crane that has never migrated north after being severely injured in April 2004 when it was a juvenile. A blow to the head (possibly from a snake bite) apparently has knocked the "migration urge" right out of that bird.

Predictions: Staying or Going?
Wouldn't it be exciting if the Lobstick crane decides to follow its two companion cranes to Canada? However, my guess is that the trio of cranes are the same 3 that spent all last summer at Aransas and could over-summer once more. The single crane sighted on Matagorda Island was reported as appearing "unbalanced and lacking power in one wing" when it was making a short flight. Is the wing injured? Or perhaps was the bird simply hit by a gust of wind and looked a little awkward on its short flight? It is possible that this bird will spend the summer at Aransas, but maybe not; I've had whooping cranes start the migration in May before.

What If. . .They Fail to Migrate?
I've had a few people express concern about Aransas whooping cranes that may become nonmigratory. What if they do? Would they influence other cranes to stop making the long and difficult migration trip? Would this hurt the population? My thinking is just to see what happens. No nonmigratory subpopulation has been established yet in 70 years of monitoring the whooping cranes at Aransas. I don't know if whoopers could nest successfully at Aransas due to predation by bobcats on the hatched chicks. But maybe they could, since the Florida nonmigratory whoopers also have lots of bobcats around and they are able to raise chicks.

Advantages of Migrating
In the case of waterfowl, a few ducks sometimes stay behind and nest here in Texas instead of migrating north. They are probably not as successful at raising young as the other ducks that migrate north, so the numbers of ducks that fail to migrate every year remains extremely small. If birds that fail to migrate are more successful raising young than those that migrate, then a species would eventually have more and more birds become non-migratory. The fact that this has not happened is proof that it is an advantage for a species to migrate due to the favorable conditions for nesting and raising young that they encounter up north during the summer.

Counting Stragglers — Or Not
Next week I hope to tell you how many Whooping Cranes, if any, are left at Aransas (after my next scheduled flight on May 10th).

 

Tom Stehn
Whooping Crane Coordinator
USFWS

 

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