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Crane Migration Update: March 13, 2001
Today's Report Includes:
- Are They Leaving Already? Challenge Question #4
- Try This: Crane Population Graph
- Crane Numbers: Challenge Question #5
- What Do You See? Challenge Question #6
- Teacher Tip: Two Timely Lessons
- Discussion of Challenge Questions #1. #2, and #3
Are They Leaving Already?
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Migration Route |
Dear Journey North,
On my last weekly aerial census flight March 8 on which I tried to find all 176 wintering whooping cranes, I came up WAY SHORT. I only counted 154! I did find all 7 family groups (two adults with their chick hatched last summer), and found about 40 other territorial pairs.
I felt fairly confident that one territorial pair was definitely missing and may have started the migration. In all, an estimated 10 whooping cranes may have departed the wintering area and headed north.
Whooping cranes normally don't start the migration until the last week in March or first two weeks in April. It would be unusual if 10 whooping cranes have started north this early. However, food continues to be short here at Aransas. The blue crabs just aren't available for the cranes to eat, so they are forced to eat clams. Imagine swallowing clams whole and relying on your gizzard to grind up all that shell and salvage a little bit of nutrition from the little piece of meat inside a clam!
Are you ready for a Challenge Question?
Challenge Question #4:
"If foods are short on the wintering grounds and the whooping cranes are not getting enough nutrition (as is the case this year), in what way will the migration be affected?"
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 daylength and not food.
d) Some of the birds won't migrate at all due to illness.
(To respond to this
question, please follow the instructions below.)
Tom Stehn, Whooping Crane Coordinator
U.S. Fish and Wildlife Service
Aransas NWR
Try This!
See our graphing activities and data analysis tips using the whooping crane population data from 1940 to the present. After the winter's low crane count, it is a good reminder of the tenuous status of this endangered species.
Crane Numbers
Why are there fewer cranes this year? Last week's report got us all thinking about this question. (See Discussion of Challenge Question #1, below.) With today's report, the plot thickens. Brian Johns, Wildlife Biologist, said low rainfall last summer at Wood Buffalo National Park in Canada led to parts of the nesting area being very dry by mid August. Brian had this to say about last year's low numbers in the breeding season:
"The total known nesting attempts in 2000 was a record 51. By mid June many of the wetlands in the Klewi River area were dry, making the young cranes more vulnerable to predation as the crane families searched for aquatic foods. With 51 nesting pairs it was anticipated that 40-50 young would hatch. However, only 30 young cranes were accounted for. Surveys began about 10 days after the first chicks hatched so there were likely additional chicks hatched that were not seen. Two pairs hatched two young (twins). Losses of young continued over the summer so that by mid August only about 13 young were still alive. The families with twins had each lost one of their chicks by mid August as well. The number of nesting pairs that successfully bring a young to Texas has varied from a low of 12% to a high of 75%, with the average of about 46%.
Challenge Question #5:
"What percentage of this year's nesting attempts produced a young whooping crane that safely arrived on the wintering grounds? How does this percentage compare with the average?" (HINT: See Tom Stehn's first report, February 27, for the number of young that safely arrived on the wintering grounds.)
(To respond to this
question, please follow the instructions below.)
What Do You See? Challenge Question #6
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Challenge Question #6:
"Look carefully at the ground in this photo. What do you think Tom Stehn (left) and Brian Johns have found?"
(To respond to this
question, please follow the instructions below.)
Teacher Tip: Two Timely Lessons
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Food supply has been a big part of the cranes' story this year. Perhaps your students will now stop to think about how the food chain changes with the seasons. This lesson will help your students see the central role that sunlight plays in living systems.
Why Fewer Whooping Cranes? Discussion of Challenge Question #1
"Why are there FEWER whooping cranes in the population this year? What different reasons can you find that explain why the number is so low?"
Tom Stehn's full report described the effect of the drought Texas had last spring and summer. The drought caused a shortage of blue crabs, the cranes' most nutritious and favorite food. A shortage of fresh water flowing into the bogs changed the salinity, cutting down blue crab reproduction. Not having enough of the highest quality food in their diets may have affected the cranes' winter health, as well as their abilities to successfully nest. To make the natural drought even worse, human uses took much of the water from the rivers, reducing the water that reached the bogs. It's a situation that threatens to get worse as more people move to Texas and place more demands on the water supplies.
You're the Scientist: Answers to Challenge Question #2
"Which TWO of these calls are given by the SAME pair of cranes?"
This question took a good ear, and we're cheering for Kenneth and also Chris, Michela, Brian, and Melissa from grade 7 at Iselin Middle School. They all said calls #1 and #3 are given by the same pair of cranes.
That's exactly right! Dr. Wessling will be proud of you!
Just in Time: Discussion of Challenge Question #3
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Voiceprints are a valuable discovery for safe, non-invasive monitoring of cranes. Thanks to the work of Dr. Bernhard Wessling, we now know that individual voices can tell us which crane is which. Voiceprints are reliable ways to identify cranes without expensive banding, stressful capturing, or risk of losing ID bands. This photo shows Dr. Bernhard Wessling with a wind-proof microphone. The shaggy mane over the microphone eliminates wind buffeting and provides for excellent quality recordings of the crane calls.
How to Respond to Today's Challenge Questions:
IMPORTANT: Answer only ONE question in each e-mail message.
1. Address an e-mail message to: jn-challenge-crane@learner.org
2. In the Subject Line of your message write: Challenge Question
#4 (or #5 or #6).
3. In the body of EACH message, give your answer to ONE of the questions above.
The Next Crane Migration Update Will Be Posted on March 27, 2001.
Copyright 2001 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form
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