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  • Whooping Crane Migration Update: April 24, 1997

    To: Journey North
    From: Wally Jobman, USFWS
    Date: April 23, 1997

    "April 17 was a big migration day. Most of the sandhill cranes which were still along the Platte River in Nebraska, as well as the whooping cranes which were known to be on the ground, left on the 17th. The 17th was clear and warm with a south wind. Good migration conditions continued until Sunday, April 20, when cool temps, rain showers, and low clouds returned. The forecast says the cool, damp weather will continue throughout this week.

    "Although not many whooping cranes have been confirmed in the Dakotas, many should be migrating through those states now. They are probably just stopping overnight and in most instances are not observed or are not reported. The following confirmed sightings have been reported to the Grand Island Field Office during the past week:"

    Wind, Weather and Whooping Crane Migration
    This map shows weather conditions in the Great Plains on April 17th. The yellow arrows indicate wind direction. (The tails of the flags show the direction the wind was coming from.) As you can see, the wind was blowing out of the south in Nebraska, just as Wally Jobman observed on the ground. In fact, south winds were blowing all across the Great Plains on this day, from Oklahoma all the way to southern Manitoba. A perfect time to fly!

    Notice the high pressure cell above Missouri; as shown, the wind moves clockwise around high pressure. In contrast, note the low pressure cell in SW Kansas; wind moves counter-clockwise around the low pressure. Thus, between the high and the low, the wind blows from the south.

    Meanwhile, Still on the Wintering Grounds in Texas.... Tom Stehn--and the final 22 whooping cranes of the flock. As Tom reported in his update last week, 100 cranes started migration April 9th and 10th. "I have heard of the sightings in Kansas and Nebraska (see today's migration data), so the whoopers that left Aransas around April 10 are right on schedule; 1 week later they're in the central U.S." How many of the cranes that left Texas on the 10th do you suppose are in Wally Jobmans' list today?

    Here Tom summarizes his April 17th whooping crane census:

    "An aerial survey of the Aransas NWR and surrounding areas made April 17th located 21 adult and 1 young whooping crane. The total population estimated still on the wintering grounds is 22. An estimated 33 cranes started the migration since the last flight April 10. The best conditions for migration since the last flight were on April 11. All other days during the week were not favorable, with unusual cool weather and frequent north winds.

    "One family group is still present at Welder Flats. The other 19 birds are all unbanded subadults. Thus, 49 out of 50 adult pairs have migrated. The juvenile crane that was left behind on the refuge on the refuge has apparently started the migration.

    "A blue crab count on April 16 found quite a few small blue crabs in the crane marshes. Crab numbers were believed to remain adequate for the cranes throughout the 1996 & 97 winter. Marsh salinities have dropped remarkably with the record March rainfall (13.86 inches) and were measured at 5 parts per thousand. Tides have dropped back to average levels."

    April 11, 1997
    Now it's Your Turn
    This map shows weather conditions on April 11th. Look at the wind directions indicated at various places along the whooping cranes migratory path. Then see if you can answer this Challenge Question:

    Challenge Question # 3
    "According to Tom Stehn, the best winds for migration from the Texas Gulf Coast (Aransas NWR near Austwell, TX) occurred on April 11th. How far does it appear the cranes were able to travel before they encountered winds from the north?"

    How to Respond to Journey North Whooping Crane Challenge Question # 3

    1. Address an e-mail message to:
    2. In the Subject Line of your message write: Challenge Question # 3
    3. In the body of the message, answer the question above.

    Don't Forget!
    Please include the name of your school and your location so we can credit you properly for your answers.

    The Next Whooping Crane Migration Update Will be Posted on May 1, 1997.