Journey North Whooping Crane Spring 2004

Tom Stehn Reports from Aransas: April 2, 2004

Tom Stehn and Survey Plane at Aransas NWR

Dear Journey North,

We had some great migration weather March 26-28 with winds gusting up to 30 mph from the southeast. I remember what the weather was like because I took advantage of the strong winds and went windsurfing 3 days in a row. Apparently about 20 whooping cranes also liked the wind and used it to begin their 2,400-mile migration. Southeast winds provide the cranes strong tailwinds that push them north at anywhere between 30 and 60 mph. When winds are unfavorable, cranes are patient and will simply wait on the ground foraging on grain, insects, or marsh critters until the winds switch around.

Restless Cranes Aloft
On my aerial census flight on March 31, I was flying along over the refuge and saw 2 cranes take flight as we approached. We circled high above them to see what they would do. The cranes circled higher and higher on thermal currents, but were staying in the same location without making any progress to the north. Winds were from the west, which would have been a headwind if they tried to migrate to the northwest. The cranes got up as high as 700 feet above the ground. After watching them soar for 10 minutes with hardly any wing flapping, I concluded they were NOT starting the migration and we quickly resumed our census. One hour later, we watched a family group of 3 cranes (two adults with their young) take flight, spiraling up to 1,500 above the ground. At this point, they were climbing faster than the airplane and they got above us and we lost sight of them. Rather than share airspace with endangered birds, and not wanting to take any chance of hitting them, we quickly descended and resumed the census. Again, the cranes did not seem to be making much progress to the north with winds still unfavorable for migration. I think in both these cases, the cranes were showing their "restlessness" and that they were "ready" to migrate, but the conditions were not quite right.

Tomorrow the weather should be very good for migration, so it will be interesting to see if these particular cranes are gone next week when I do my next flight.

How Many Whooping Cranes?
On my March 31 census flight, I counted 167 cranes. Thus, a maximum of 26
cranes out of the flock of 193, or 13%, could have migrated. I probably overlooked a few cranes on the census flight, so I'm guesstimating that about 20 whooping cranes have migrated, or 10% of the flock.

Answer to Challenge Question #6
I asked you last week why whooping cranes start migration about one month later than their sandhill cousins. The snows have just recently melted in the prairie provinces of Canada, so the whooping cranes would do just fine if they were 1,500 miles north of Texas right now. Over one-half million sandhill cranes are currently on the Platte River in Nebraska, an important staging area for sandhills. (Staging refers to an extended stopover for a migratory species.) Sandhill cranes gather together on the Platte for over a month, forming big flocks, selecting mates, and building up energy reserves before they push on to the north. Whooping cranes don't have a staging area in the spring. When they get to the Platte River, they may stop for a few days, or may just continue flying, depending on weather conditions. Since the whooping cranes don't "stage" in the spring, they thus can leave later from their wintering grounds and still get up north about the same time as their sandhill cousins do. This late departure helps the whooping cranes, because high spring tides and warmer temperatures allow blue crabs at Aransas to move from the bays back into the crane marshes. One whooping crane will eat up to 80 blue crabs a day when available. Blue crabs are the favorite food of whooping cranes and this crab feast in March is an important opportunity for the whooping cranes to build up energy reserves needed for the long migration.

Tom Stehn, Whooping Crane Coordinator
U.S. Fish and Wildlife Service
Aransas NWR
Austwell, Texas