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Whooping Crane Migration Update: April 24, 2001

Today's Report Includes:

Cranes Reaching Canada!

Migration Route
Map by Claudia Fonkert
Macalester College

Brian Johns sent this news flash from the northern end of the migration trail: "The first birds are starting to arrive in Canada! There have been reports from the southern portions of Saskatchewan. April 18, two birds were sighted near Last Mountain Lake. Two birds were seen near Regina on April 19; a pair was observed near Weyburn on April 21; and a single was observed flying with Sandhill Cranes on April 21 near Colonsay, Saskatchewan. In south-eastern Saskatchewan there are good water conditions, but it is much dryer as the birds move north into central Saskatchewan. I am expecting that some of the traditional spring stopover locations will not be used this spring due to lack of suitable wetlands for roosting. I will have a habitat report on the breeding grounds for the next update."

Pull out your map and pinpoint the locations Brian mentioned. When strong tailwinds are combined with thermals, the cranes can travel about 420 miles in a day. This information, together with daily weather maps (see link below) will give you good clues as to when the cranes arrive back on territory!

Tom Stehn's Crane Countdown
Tom Stehn
Tom's most recent census flight was April 17th. He had predicted finding fewer than 50 birds. Now we know where some of them are! Here's Tom's report:

"An aerial census of the Aransas NWR and surrounding areas made 17 April, 2001 estimated the number of whooping cranes currently present at Aransas at 20 adults + 1 young = 21. It is estimated that about 153 cranes have started the migration. The current size of the Aransas / Wood Buffalo population is estimated at 174. The peak population during the 2000-2001 winter was 180. An estimated six whooping cranes died at Aransas this winter."

Recap of cranes observed: (20 adults + 1 young)

Location

Refuge

Lamar

San Jose

Matagorda

Welder

Total

# Adults

2 + 0

0

5 + 0

10 + 1

3 + 0

20 + 1 =

         

Total

21

Challenge Question #16:
"According to the latest aerial census, what percentage of the flock has migrated?"

(To respond to this question, please follow the instructions below.)

Tom wrote, "All whooping cranes present on today's flight were thought to be subadults. One chick was present by itself on Matagorda and not near any other cranes. This chick was part of a single parent family throughout the winter. The census airplane made the chick nervous and it flushed a short distance on two of the three approaches by the airplane. This type of behavior was not noticed all winter and demonstrates how the behavior of a juvenile changes dramatically when it is no longer with its parents.

"An ongoing blue crab census indicates that crabs are finally moving back into the marshes. Tides became higher at the end of March, and were extremely high April 10-11. This movement of crabs was basically too late to help the cranes substantially before their migration. Marsh salinities are 23-25 ppt, but bay salinities are lower, measured at 15 at the refuge boat canal on April 16."

Going. . . Going. . .Almost Gone from Aransas!
Tom sent the following letter on April 19, two days after his flight.

Dear Journey North,
I am so glad the whooping cranes have apparently left on schedule for their summer home in the Northwest Territories of Canada. An aerial count I did on April 17 found only 21 whooping cranes still at Aransas. These all appeared to be non-breeding birds that just aren't in as much of a rush to get north as the breeding pairs. I estimated that up to 119 whooping cranes have migrated since the previous flight on April 4. Migration conditions have been very good throughout that period. This is basically "on schedule." I'll give the cranes another 10 days before I fly again on April 27 to see if any are still here on the Texas Coast.

One of the birds remaining at Aransas is a juvenile. This bird had been part of a single-parent family all winter, one of the adults having died after nesting last summer. This juvenile was acting extremely nervous, taking flight for a short distance as our airplane approached. Normally the cranes don't pay much attention to the airplane since our disturbance as we fly past is such a quick event, but without Mom or Pop around, the juvenile's behavior changes dramatically when it is on its own. It has to be much more alert to survive. But this bird will be fine and knows the migration route. I fully expect it to return to Wood Buffalo National Park this summer, and it may make the entire migration by itself.

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

Find Tom's complete letter here:

Do you suppose the lone juvenile crane is eating his fill of delicious blue crabs? The young crane learned the migration route from Canada to Texas last fall. When this crane returns to the nesting grounds this spring, will it be nesting? (If you donít know the answer now, you'll find out in our next report.)

Try This! A Good Week to Fly?
Tom has told us that cranes usually depart when high-pressure systems bring sunshine to Texas and winds from the south or east. Thermals and strong southeast winds provide ideal migration conditions. The least favorable conditions for crane migration are low-pressure systems with north winds because low-pressure systems are associated with storms. Watch the weather conditions in Texas this week to see whether conditions are good for the last cranes to go. Then follow the weather in Canada to see if you can tell whether the cranes get a "good welcome" this year. These daily weather maps will help you analyze the weather:

NOTE: There is no reporting station in NE Alberta at Wood Buffalo where the nesting grounds are. The nearest is about 150 miles to the south. At each reporting station (marked by yellow circle with arrow) the temperature is the number shown at "10 o'clock."

Who's Who?
We asked Brian Johns, wildlife biologist at the cranes' nesting grounds, how he recognizes the mated pairs that return each year. Brian said, "The mated pairs are identified in two ways. From 1975 to 1988, young were banded with coloured leg bands. These bands are still visible on some of the adult birds and they can be identified. In addition, the cranes each have a territory that they return to each year. New pairs seek out territories adjacent to older established pairs, or sometimes they may move into a completely unoccupied marsh. The unbanded pairs are the hardest to keep track of, especially if they move around within their territory."

Talking About Territories
Crane on Nest.
Photo Courtesy Dalton Muir, CWS
By our next report, many whoopers will be back on territory. What's next? Brian Johns describes what the whoopers do when they arrive on their traditional nesting grounds:

"The cranes feed along the way north, and usually arrive on the breeding grounds with enough fat reserves left after their 4000 km long migration that they can nest soon after arrival. When they arrive on the breeding grounds they will carefully scout out a location for this year's nest.

"The pairs each defend a territory on the breeding grounds from other whooping cranes. Within their territory they will look for a suitable nest site. It will be one that contains nesting material (bulrush, sedge or cattails) and the right depth of water (usually about 15-30 cm of water, most often in the 20-25 cm range).

Click to enlarge and see eggs
Photo Courtesy Brian Johns, CWS
"The cranes build a new nest each year. Sometimes they may nest in the same wetland as a previous year. Other times they may move to a completely new part of their territory. The territory sizes vary depending on how close their neighbours are. Average territory size is about 5 square km."

Challenge Question #17:
"How big is 5 square km? Name something familiar to you that is about the same size as a crane pair's territory."

(To respond to this question, please follow the instructions below.)

Nice Nest!
Crane on Nest. Photo Courtesy Dalton Muir, CWS
Brian says, "The nests are built in water and are about 1 metre across. Some nests are built from the bottom of the pond up, while others are floating nests. The top of the nest is usually about 10 cm above the surface of the water. Preferred locations are ones that contain suitable nesting material, such as bulrush, sedge or cattails in about 15-30 cm of water."

Challenge Question #18:
"Why do you suppose cranes build their nests as described above?"

(To respond to this question, please follow the instructions below.)

Safe at Night: Discussion of Challenge Question #14
Crane standing on one leg
Photo Courtesy Brian Johns, CWS
With whoopers flying between Texas and Canada, Tom Stehn asked you to think about this: "What do cranes look for when searching for a place where they'll feel safe spending the night?"

There's plenty to think about! Tom says, "Cranes want to spend the night, or roost, in shallow water normally between 1 and 1-1/2 feet deep. That way, they will hear any predator approaching as it splashes through the water and be able to fly away in time. This roost pond, marsh or shallow river has to have an open view and can't have vegetation taller than the cranes. Thus, wooded areas are not usable. It also should be away from roads or buildings where cranes could be disturbed by humans. The roost area either should contain aquatic foods for the cranes, or be located nearby to agricultural fields where the cranes can eat waste grains. When they find a good roosting area, the cranes stand (sometimes on one leg) throughout the night, often sleeping with their head tucked under their wing." Tom adds, "I don't think I would make a very good crane since I'd have trouble sleeping while standing up." (How about YOU?)

Predicting Crane Production: Discussion of Challenge Question #15
We asked: "What factors affect how many young whooping cranes are produced in a breeding season?"

Writing from the cranes' breeding grounds in Canada, wildlife biologist Brian Johns listed these possible factors:
  • The number of pairs actually nesting
  • The number of viable eggs produced
  • Weather conditions at time of hatch and in the ensuing 2 weeks
  • Overall habitat conditions (water levels)
  • Abundance of food
  • Abundance of predators
  • Abundance of other prey items (for the predators to eat)
  • Likely a number of other things we haven't even though of

How does your list compare to Brian's list? Did you think of likely reasons that weren't on Brian's list?

Note To Teachers: We'd Appreciate Your Thoughts!
In our May 1 update, we'll be asking for your feedback on the Journey North program. Watch for our Year-End Evaluation Form and please plan to take the time to send your suggestions and comments. The information you provide at the end of each year is the single most important tool used to guide our planning.

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 # 16 (OR #17 OR #18).
3. In the body of EACH message, give your answer to ONE of the questions above.

The FINAL Crane Migration Update Will Be Posted on May 8, 2001.

Copyright 2001 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form

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