Whooping Crane Whooping Crane
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Update from the Whooping Cranes' Winter Headquarters
Aransas National Wildlife Refuge
Austwell, Texas
March 27, 2001

Dear Journey North,

My best way of monitoring the whooping crane population is on weekly aerial census flights when I try to find all the whooping cranes and plot their location and type of habitat they are using. We fly in a Cessna 172 high-wing aircraft at about 90 miles per hour just 200 feet above the ground. Using a Global Positioning System (GPS) unit that tracks our path, we fly precise transacts about 3/8's of a mile wide until, about 7 hours later, we have seen all the salt marsh where the whooping cranes winter. I plot all the crane locations on aerial photographs that helps me make sure that the whooping cranes aren't moving around during the census flight and being counted twice. The flying is done by Dr. Tom Taylor, a former college chemistry professor who now flies full time. I just hang on and look for cranes. Last year, Tom had heart bypass surgery and I really missed flying with him. This year he is back. Two weeks ago, it was time for the airplane to have heart surgery. After 2000 hours of flying, regulations require that commercial Cessna aircraft get their motors replaced. After all, they have flown over 200,000 miles during that period of time. With the airplane just having one engine, it has to be 100% reliable. So now I have the secure feeling of knowing that the aircraft engine is brand new.

Census flights March 15 and March 21 indicated that just about all the whooping cranes are still here. I found 171 whooping cranes the first flight, and 168 the next. Probably just missed a few on both flights. On both flights, one territorial pair was missing and could have migrated. So far there has been only one whooping crane sighting reported anywhere in the Central Flyway, another good indication that just about all the whooping cranes are still at their winter home. Due to a storm system that reached the Texas coast last weekend, the strong north winds dramatically lowered water levels in the bays and marshes. The cranes responded by moving from the vegetated salt marsh to the shallow bay waters probing for clams, mud shrimp, and bloodworms.

Unfortunately, these foods are not as nutritious as blue crabs, the main food that makes up 80-90 % of the whooping crane diet when blue crabs are abundant. With the scarcity of blue crabs this year due to the summer drought hurting blue crab reproduction, I believe the cranes have actually lost energy throughout parts of this winter. I don't think they have consumed enough energy and built up enough fat reserves to have a very successful nesting season this spring. Some of the pairs may not even attempt to nest if they are not in good enough condition.

I asked in my last report how the lack of food this winter might affect the spring migration. These were the four possibilities I had thought of:

a) The birds will leave early hoping to find more food during the migration.
b) The birds will leave late since their energy reserves are not sufficient for the trip.
c) The birds will leave on time since the migration is governed by day length and not food.
d) Some of the birds won't migrate at all due to illness.

My guess is c)--the birds will leave on time. Not only do birds have an excellent compass and GPS system in their head that allows them to travel across North America; they also have a very accurate internal clock. As the days become longer in the spring, the cranes somehow can sense the longer days and know when it is time to leave for the north. If they leave too early, they will encounter frozen conditions and find less to eat during the migration. If they leave too late, they won't have enough time to raise their young before fall blizzards arrive.

If either b) or d) were your choices, I might have to agree with you. Some crane researchers believe the cranes will tend to leave on the late side when their energy reserves are low. And it is certainly possible that one or two cranes may not migrate at all due to illness, or for some other unknown reason. The only answer I would disagree with is a). I don't think the birds would leave early to find more food since seeking food is not a motivation for migration. And even a poor food winter in the Texas coastal marsh would have more food available than a frozen marsh or wheat field in North Dakota.

I'm probably going to get one more complete aerial count of most of the cranes next week on March 29. After that, the migration will start with numerous cranes expected to depart the first two weeks in April. I'll estimate when they leave and compare it with past years to see if they depart on schedule.

Tom Stehn, Whooping Crane Coordinator
U.S. Fish and Wildlife Service
Aransas NWR
P.O. Box 100
Austwell, TX 77950

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