Tom Stehn Reports from Aransas: March 14, 2003
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Tom Stehn and Survey Plane |
Just when I thought things were looking up, a whooping crane chick turned up missing and was presumed dead on my census flight on March 6. Since chicks stay with their parents throughout their first year, finding the parents on their winter territory with no chick around almost always means the chick has died. We did not find the dead crane, but that is almost expected since carcasses are usually scavenged by vultures and racoons with 48 hours. I have no idea what caused this mortality. This loss leaves 184 whooping cranes wintering in Texas, still a significant increase from the 173 present last spring. I sure hope that 2003 brings a similar large increase in whooping crane numbers.
One of the things I do every winter is monitor foods available for the whooping cranes to eat. This year, volunteers are helping me do a blue crab survey every 3 weeks. They hike the marsh for an hour just as a whooping crane would, stalking blue crabs. Last week the volunteers counted 102 crabs, quite a picnic after an hours worth of effort for a whooping crane that can eat up to 80 blue crabs a day. The blue crabs currently in the marsh are between 2 and 3 inches in size, just right for a whooping crane to gobble down and probably even swallow whole, shell and all. Their gizzard is able to grind up all that shell, and they digest the blue crab meat that is high in protein and fat. With the abundance of blue crabs in the marsh this winter providing the cranes with "grocery store" ponds overloaded with their favorite food, the cranes have done very well and are in excellent condition. I expect them to have a very productive nesting season if they can survive the hazards of the spring migration.
My census flight on March 12 was cut short after 2.5 hours due to fog that just wouldn't go away. We just barely made it back to the airport before the fog really rolled in. Thus, there wasn't enough time to find all the cranes. However, its really too early for any of the cranes to have started the migration, and the weather has also not been favorable for starting a migration. It's still snowing in the northern U.S., right where the cranes will have to migrate through. How do you think the cranes "know" that it is still too early to start their migration? What clues do they use to inform them? One key to the answer is that they start the migration about the same time each spring, so think about what changes at the same rate every spring.
Talk at ?cha next week.
Tom Stehn, Whooping Crane Coordinator
U.S. Fish and Wildlife Service
Aransas NWR
P.O. Box 100
Austwell, TX 77950
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