Whooping Crane Migration Update: April 11, 2000
Cranes Overhead! Tom Stehn's Crane Countdown
Aransas National Wildlife Refuge
April 7, 2000
Dear Journey North,
An aerial census of the Aransas NWR and surrounding areas made April 07 located 20 whooping cranes.
The Lone Chick Leaves
Nuking Winds and a Record Week
An estimated 149 cranes have started the migration since the last flight on March 30. This is the largest number of cranes ever leaving in an 8-day period that I can recall. Weather was unsettled April 1 and April 2 with clouds. Strong north winds were present April 3 as a low-pressure system crossed the Texas coast. As the next low approached Texas, strong south winds developed blowing from the coastal high pressure in Texas towards the approaching low out west. Skies were clear and south winds started to pick up throughout the day on April 5. Many whoopers departed that day. The whooping crane tour boat captains noted very few cranes present that afternoon. More cranes presumably started the migration the following day as the pressure gradient strengthened and winds howled up to 30 miles per hour on the refuge. I left work early and went windsurfing to take advantage of the "nuking' winds, as they are described in windsurfer lingo.
Ideal Migration Conditions
With clear skies providing thermal currents, and the winds providing a push from behind, the cranes had ideal migration conditions. With these conditions, most of the cranes that departed April 5 and 6 would have crossed just about all of Texas in one day. This is why we rarely receive reports from Texas of whooping cranes in the spring. They typically will only spend one night in the state. The whoopers have been known to fly from the refuge to just past Wichita Falls, Texas near the border of Oklahoma in one day, a distance of over ____ miles. Can you fill in the blank to answer:
(To respond to this question, please follow
the instructions below.)
USFWS Whooping Crane Coordinator
Keep Your Eyes on the Skies
Now that the migration has begun, plan to keep a close eye on the skies of the Central Plains. April brings whooping crane migration updates every Tuesday, so you can follow their progress closely. You'll need these daily weather maps to analyze the weather:
According to Tom Stehn, 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. In fact, all along their migration path, the whoopers wait for high pressure and favorable winds to continue their migration.
The least favorable conditions for crane migration are low-pressure systems with north winds. This is because low-pressure systems are associated with storms. When the migrating whoopers encounter these storms with their north winds, the birds will quickly find a place to land. They'll wait for several days until the north winds rotate back around to the south.
During these storms, the whoopers will make short daily flights out to grain fields to feed, returning to wetlands where they will spend the night. It is during these short low altitude flights where they might collide with power lines and be killed, especially during rain or snowstorms when the power lines are not so easily seen.
Next Stop: Platte River
"With the exception of the 1 or 2 whooping cranes which arrive early with the sandhill cranes, most migrating whooping cranes do not spend much time in Nebraska. Most birds seek out a roost site late in the afternoon and may fly to a field to feed before roosting. The following morning they will feed and then continue migration by 10 a.m. The breeding pairs are especially in a hurry to get to the breeding grounds. During their stopover, they feed in cropland (probably eating waste grain), grassland (feeding on invertebrates such as beetles and earthworms), and wetlands (feeding on frogs, fish, etc.). Since the birds do not stop long, they are usually seen by only a few people. We believe many birds are not seen at all during a stopover, and therefore are not reported. Many sandhill cranes left the Platte River on April 4. It appears that the single whooping crane which had been here since early March also left on migration."
Canadian biologist Brian Johns, of the Canadian Wildlife Service, will share the excitement when that single whooping crane-and all the other whoopers--arrive once again on their traditional nesting grounds. Stay tuned!
News Flash: Fate of the Hatchlings
One of the Florida whooping crane chicks we wrote about in "Hooray for Hatchlings" last week has disappeared. Henry Cabbage of the Florida Fish and Wildlife Conservation Commission (FWC) told Journey North: "We don't know what happened to the chick. There are all kinds of predators and perils. Bobcats do a lot of the crane predation. Alligators and predatory birds take cranes, too. The good news is that the surviving chick is now more than 3 weeks old. The chicks are most vulnerable during the first two weeks of their life, so chances are good that the surviving chick will live at least until it is 75 days old. That's when whooper chicks learn to fly, which is another very risky time for them."
Three whooper pairs in the nonmigratory Florida flock have nested so far this year. One nest was abandoned and a second produced the two chicks we wrote about in "Hooray for Hatchlings." A third pair of whoopers also abandoned their egg because they were 'just too young to be good parents.' The female that laid the egg was only 34 months old. It is unheard of for female whooping cranes to mate until they are 4 or 5 years old." This makes us wonder:
Mates for Life: Discussion of Challenge Question #8
"Do bonded cranes, who mate for life, ever split up? If so, why?"
Tom Stehn says the answer is yes. "Paired whooping cranes do split up occasionally. This happens most frequently when an older male loses a mate because of mortality. This older dominant widow male will then sometimes break up a younger pair and re-pair with a younger female. Does this remind anyone of human behavior?"
In 1996, Tom wrote to Journey North about a bonded crane pair that had a rocky relationship. Read about the "whooping crane divorce" that later became a reconciliation and family success!
Answer to Challenge Question 12
Challenge Question #12 asked, "How many whooping cranes were in the reintroduced flock as of March 29, 2000?"
The answer, 67, was in "Hooray for Hatchlings: "Researchers have released 183 whooping cranes into the wild during the past seven years. Mortality was high at first, but 65 of the birds are still alive...67 counting the new chicks."
Crane Countdown: Answer to Challenge Question #13
"This is only 7.5 % of the flock." (14 cranes out of 188.)
Lonely Chick? Response to Challenge Question #14
"What do you think will happen to the chick left behind at Aransas?"
You know the good news about the chick already after reading Tom's report above. It's a happy outcome that most of you didn't expect! Students from Iselin Middle School 7A thought that the chick would die:
Chris Gioiello and Andrew Dorward said, "Because the chick is so small and didn't start off with his parents hewill not be able to find his way." Jonathan Varela thought the chick would die "because the chick doesn't have protection from its mother. Also, it is probably not mature enough to fly and find its way or to be able to get it's own food. (firstname.lastname@example.org)
Tom Stehn had an answer for our question too: "It has to get a very quick education. The chick immediately learns that all other cranes will chase juveniles since the chick is at the bottom of the dominance ladder. Several days ago, another researcher observed this chick being chased by other whooping cranes. The chick flew off and landed by itself. Over time, the chick will learn how to mingle with other cranes and give ground but not have to fly off. Thus, the chick may join other non-breeding cranes, which we call subadults, and may migrate in a group back towards Canada. But it is also possible the chick may remain by itself and successfully make the migration all the way back to the nesting grounds on its own."
Up, Up and Away: Response to Challenge Question #15
"What might be some advantages for whooping cranes to migrate in very small groups rather than in big flocks?"
One advantage is fewer of the birds would get hurt if an accident occurs. The cranes can't afford for a large group of them to die. Finding food is easier for a smaller group than for a whole flock. Smaller groups can fly at different rates to help the inexperienced flyers. Cranes traveling in small groups can hide more easily from predators that might kill them. And it might be easier for a small group to find a place to rest.
Who Gives a Whoop? Response to Challenge Question #16
Last time we said a whooping crane's call can be heard up to two miles away. We asked: "What feature of a crane's anatomy enables the call to be so loud? And what are some reasons why cranes call?"
The long-distance loudness comes from the bird's 5-foot-long trachea (half of which is looped within the keel of the breastbone). The crane's breathtaking bugle is created by resonance in that l-o-n-g trachea. Cranes may call to communicate danger, to defend territory, and to reinforce pair bonds. Wally Jobman adds, "It has been my experience that whooping cranes do very little calling during migration. They will often call when they take flight, but do little calling during migration flights. They're certainly not as noisy as the sandhill cranes. Whooping cranes do find each other during migration (e.g., a group of 3 may be joined by a group of 2 during migration), and one could speculate that calling may be a means of locating other birds during migration."
How to Respond to Today's Challenge Questions:
Please answer ONLY ONE question in EACH e-mail message.
1. Address an e-mail message to: email@example.com
2. In the Subject Line of your message write: Challenge Question #17 (or #18).
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 April 18, 2000.
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