Whooping Crane Migration Update: March 14, 2000

Today's Report Includes:

One Mystery Solved: Latest News from the Wintering Grounds
Aransas National Wildlife Refuge
Austwell, Texas
February 29, 2000

Dear Journey North,
"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."

Why Fly?

Challenge Question #4:
"When do young whooping cranes leave their parents for the first time? And since migration is so dangerous, why do you think the juveniles migrate 2,600 miles to the north if they're not going to nest?"

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:

 Migration Route Map by Claudia Fonkert Macalester College
Last time Tom said the first whooping cranes normally start the migration about mid-March, but a few could leave a little before that. Join Tom in tracking the migration, using the aerial flight census reports in each Journey North Update. We've provided a reproducible log sheet to record the number of whooping cranes that start the migration with each report. See:

(NOTE: You'll want to use the figure reported by Tom in today's report for a total of 188 cranes wintering at Aransas.)

Solo Whooper:
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

Challenge Question #5:
"How can you tell the difference between an adult plumaged whooping crane and a juvenile or young-of-the-year crane?"

Challenge Question #6:
"Why might a whooping crane choose to winter with sandhill cranes?"

Crane Count:
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.

Discussion of Challenge Questions #2 and #3

Last time we asked Challenge Question #2, "When standing, cranes look like they have knees that bend backwards. Can cranes really bend their knees backwards?"

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:

Challenge Question #7:
"Name at least one other adaptation of a whooping crane's body. Why do you think it has that adaptation?"

How to Respond to Today's Challenge Question: