Whooping Crane Migration Update: March 14, 2000
One Mystery Solved: Latest News from the Wintering Grounds
Aransas National Wildlife Refuge
February 29, 2000
"Finally, a breakthrough! For more than two months, two family groups of whooping cranes have not been at Aransas. If they had been here, I would have identified them by plastic colored leg bands on one adult in each family. On February 29th, one of the missing family groups was right back on their territory on Central Matagorda Island. Since I had documented 185 in the flock without this family, their presence brought the whooping crane population to a record 188. This is 5 more than last winter.
See if you can follow this math. Last spring we had 183 total whooping cranes in the population. They migrated to Canada, nested and raised young, and brought back 17 juveniles. If all of the 183 whoopers had survived the summer, the flock could have reached 200 in size. Thus, since I can only account for 188, that means 12 whooping cranes died between spring and fall, 1999.
Is the loss of 12 birds unusual? Let's look at percentages. The loss equals 12 out of the flock of 183. Twelve divided by 183 = 6.5%. This mortality is not unexpected or unusually high. Mortality can run as high as 10 or even 12% of the population in bad years. Whooping cranes probably live 20-30 years in the wild, so we have to expect population turnover."
Tracking the Crane Migration
Is the loss of twelve birds unusual? Where was the missing family group between mid-December and February 29 when Tom spotted them? How many of the cranes counted on this census flight were chicks? What factors made counting cranes difficult on this flight? For these answers and more highlights, see:
(NOTE: You'll want to use the figure reported by Tom in today's report for a total of 188 cranes wintering at
Challenge Questions #5 and #6
Do you remember this statement from Tom's first report? "One whooping crane never made it to Aransas, but was wintering in West Texas with sandhill cranes." Where is that whooper now? Wally Jobman reported this news from the U.S. Fish and Wildlife Service office at Grand Island Nebraska:
"On March 2, a single adult-plumaged, unbanded whooping crane was confirmed south of Grand Island along the Platte River. This is likely the bird that wintered with sandhill cranes in west Texas. Many sandhills arriving daily now." Which leads us to
Discussion of Challenge Question #1
Last time Tom believed there were 185 cranes, so we asked: "Why are there only 2 more whooping cranes in the population this year? How many different reasons can you find that explain why the number is so low?"
A close look at Tom's report revealed these factors about the 1999 season: Much-needed rainfall came right when the eggs were hatching, and some of the very small chicks did not survive the wet, cold weather. Forty-eight nesting pairs produced 48 chicks, including 10 pairs with twin young. None of the sets of twin young survived, and only 20 chicks were still alive in mid-August. Seventeen of these survived the hazards of the 2,500-mile migration to Aransas. One whooping crane never made it to Aransas, but was wintering in West Texas with sandhill cranes.
Anatomy and Adaptation
Discussion of Challenge Questions #2 and #3
It certainly looks that way, but this labeled picture reveals the answer. Many people believe that the joint labeled "ankle" is really the crane's "knee," and that it bends backwards. Cranes, however, stand on their toes, so that all the joints of a crane's leg bend in the same direction as our leg joints. Challenge Question #3 We also said, "Anatomy is a clue to adaptation. Why might cranes' legs have this adaptation?"
Wildlife biologist Brian Johns, based at the cranes' Canadian nesting grounds, explains: "Most bird legs have the same general anatomy and function the same way. The zigzag bends in a bird's leg enable the leg to fold up so the bird can perch or gently settle down on eggs. In cranes, as in most wading birds, the foot or tarsometatarsus is elongated to enable the crane to wade into deep water in search of food without getting its feathers wet."
But this answer raises another question:
How to Respond to Today's Challenge Question:
Please answer ONLY ONE question in EACH e-mail message.
1. Address an e-mail message to: firstname.lastname@example.org
2. Important: In the Subject Line of your message write: Challenge Question #4 (or #5 or #6 or #7).
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 28, 2000.
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