Whooping Crane Migration Update: April 17, 2001 Today's Report Includes: Tom Stehn Reports: Best Flying Conditions for Cranes Safe at Night: Challenge Question #14 Heads Up Over the Platte Teacher Tip: Cracking the Code Predicting Crane Production: Challenge Question #15 Above the Clouds? Discussion of Challenge Question #11 Stay or go? Discussion of Challenge Question #12 High Wire Hazards: Discussion of Challenge Question #13 Tom Stehn Reports: Best Flying Conditions for Cranes Tom is flying today--April 17th--to see how many stragglers remain at Aransas, and you'll hear the results next week. Last time Tom predicted he'd find fewer than 50 birds on today's flight. Next time we'll see how close Tom's prediction came! Meanwhile, Tom sent us this letter, written a few days ago. Read carefully to find out the two most important conditions to help cranes in their journey north. At what time of day do they usually take off from Aransas? How far could they fly in a day? (What place is that distance from where you live?) How long does it typically take whoopers to reach their summer breeding grounds in Canada's Wood Buffalo National Park? What slows them down? "Dear Journey North, We've had great migration conditions every day the first 10 days in April. Let me try to describe the conditions that help the cranes migrate and also answer some of the questions I asked last week. Two things are most important for the migrating cranes. The first is favorable winds. The cranes want a wind either behind them or at an angle to their route so the stream of air can push them along. Leaving the coast of Texas, all the cranes so far in April that have migrated have had very strong southeast winds. "Southeast" winds mean they are coming from the southeast and thus will push the cranes to the northwest. Since the cranes' direct migration route is a compass bearing of 332 degrees (north-northwest), the southeast "tailwinds" provide them a strong push at their tail. Several times during their trip north, the cranes will encounter winds from the north or northwest, what one would call headwinds if you were trying to fly to Canada. With strong headwinds, the cranes will stop the migration and wait several days for the winds to turn around and blow from a more favorable direction. Thus, although the cranes may make it all the way to Canada in 12-14 days of flying, the total journey may take 20-25 days depending on how many days they stay on the ground waiting for favorable winds. The second key factor is thermal currents. When watching the cranes just before they start a migration flight, we always notice "heat waves," or a shimmering of air, visible through our spotting scopes about 15 minutes before the cranes depart. In the morning, as the sun heats up the land, the warmed air rises and provides lift for the cranes. This warming usually becomes strong about 9:30 AM, a typical time when cranes will start their migration flights. The cranes are lifted by these thermal currents and will rise as high as 6,000 feet in the air--more than one mile high. They then glide to the north down to about 1,000 feet before catching another thermal. When rising in a thermal, the cranes make very little forward progress. When they are gliding down, we have clocked them travelling at 62 miles per hour. When strong tailwinds are combined with thermals, the cranes can travel about 420 miles in a day. Usually about 5 PM, the thermals are dying out as the sun gets lower, and the cranes may start flapping their wings more and flying in a straight line, but soon they will get tired of that type of effort and look for a place to spend the night. That leads us to: Challenge Question #14: "What do cranes look for when searching for a place where they'll feel safe spending the night?" (To respond to this question, please follow the instructions below.) Next week I should know just how many whooping cranes are left at Aransas. I'm fairly sure most of the adult pairs will have migrated." Tom Stehn, Whooping Crane Coordinator U.S. Fish and Wildlife Service Aransas NWR Link to Tom Stehn's full report. Heads Up Over the Platte Wally Jobman, USFWS Endangered Species biologist in Grand Island, Nebraska, reports from the migration path. He says the two newest confirmed whooping crane sightings were on April 7 and 8, near Upland, NE, in Franklin County. On April 11, three birds were reported one mile south and 2 miles east of the Gibbon I-80 interchange, but the sightings haven't yet been confirmed. Why so few cranes? Wally told us about last week's weather: "Up to 8 inches of wet snow fell in parts of western and northern Nebraska on Wednesday April 11. Winds were 20-40mph, creating blizzard conditions at times." The weekend of April 14-15 was expected to bring good migration weather. Based on what Tom Stehn told you about the best conditions for cranes to migrate, check the weather maps this week and make your OWN predictions for what Wally and Tom will report in next week's whooping crane update! Link to Weather Map Archives Teacher Tip: Cracking the Code Wouldn't it be fun to know exactly which whoopers were spotted over Nebraska? After all, each individual has its own incredible life story. Thanks to the pioneering work of crane vocalization expert Dr. Bernhard Wessling, identifying individual cranes is easier on the cranes than capturing and banding was. But before Dr. Wessling's work, scientists could only keep track of individual cranes by banding them. But no whooping cranes have been banded since 1988, so most of the banded birds that still survive are difficult to identify because their bands are faded, broken, or missing. Thanks to Wally Jobman, you CAN "meet" a migrating whooper that was banded. Wally sent us all the sighting records for one of his favorite banded cranes, Crane RwR-B. Such raw data sightings are a careful collection of observations and records from which scientists can piece together the stories of a crane's life. It takes a bit of detective work and a lot of curiosity to figure it out. Studying banding data often raises more questions than answers. But that's what scientists must do each time they get a "helping" of raw data, and we're eager to give you the same challenge and adventure! What kind of story will you piece together from banded Crane RwR-B's raw data? How old is this whooper? How many times was it seen? During what summer (year) did RwR-B product its first chick? When was the first time RwR-B's nest was observed? Do you think it was RwR-B's first nest? For how many seasons does RwR-B seem to stay with a chick? Which period of time shows no record of chicks produced? See what else Wally told us about the banding program and RwR-B: Cracking the Code: Banded Cranes Tell Their Story Predicting Crane Production Migration, territory, courtship, nest building, egg laying, incubation, and care of the young--all are parts of the breeding cycle. These activities happen so cranes can pass their genes on to new generations. In an earlier report, Tom Stehn reminded us, "The peak population during the 2000-2001 winter was 180. An estimated six whooping cranes died at Aransas this winter, leaving 174. This is quite a drop from the 187 whoopers in the flock in the spring of 2000. We can only hope for a reversal of this trend in 2001." Brian Johns is a wildlife biologist on the cranes' breeding grounds in Canada. "Predicting crane production can be a tricky business, says Brian. "There are so many factors that affect the production of young." What do you suppose some of those factors are? We want to hear from you! Challenge Question #15: "What factors affect how many young whooping cranes are produced in a breeding season?" (To respond to this question, please follow the instructions below.) Above the Clouds? Discussion of Challenge Question #11 Last week Tom asked: "Do whooping cranes ever migrate above the clouds? If so, what would be the advantages and disadvantages of flying above the clouds?" Tom says cranes will not fly above a thick cloud layer the way ducks and geese do. He explains: "They will not since there are no thermal currents above thick clouds. Whereas ducks and geese continually flap their wings during migration, and thus benefit from the "thinner" air high above the clouds that offers less resistance, cranes rely on thermal currents and soaring flight patterns. Other large birds such as pelicans, hawks, eagles, and vultures also rely on thermal currents and soar in spiral patterns to migrate. Stay or go? Discussion of Challenge Question #12 Tom asked you to think about this: "Why would some of the whooping cranes be less eager than others to leave the wintering grounds?" "The answer," Tom says, "comes down to physical differences between adult birds that need to get up to Canada and nest, and non-breeding birds (subadults) that will not be breeding this summer. Subadults are cranes usually between ages 1 to 4, too young to mate. Different hormone levels can be measured in the blood in adults and subadults. Adults have much higher hormone levels, making them anxious to get north and breed. The younger subadult birds don't have those high hormone levels and thus will take their time leaving Texas. "But it's not always that simple. Sometimes subadult whooping cranes will migrate with sandhill cranes and thus be heading north in March in front of many adult whooping cranes. Adults can start the migration at vastly different times. For example, one year we had one breeding whooping crane pair start the migration in early March, and the last breeding pair left Aransas on April 20. That's quite a span of time. You don't have to worry about the cranes that leave late. Those late migrants usually make a more rapid trip to Canada so that all the adult pairs will get up to Canada in time to nest." High Wire Hazards: Discussion of Challenge Question #13 Our last update described why high wires were extremely dangerous to migrating cranes, and we told you about new little coils called Bird Flight Diverters that should help solve the problem. We asked, "Why do you think cranes have difficulties seeing wires? How do you think little coils help solve the problem?" Cranes have trouble seeing wires because nothing like wires exists in nature. Cranes have no idea of a wire's width. Since the ends of a wire are so far apart and far away from them, cranes have no idea how far they are from a wire until they get dangerously close. Coils called Bird Flight Diverters (BFDs) placed on wires can help because the coils are three-dimensional, giving cranes a better concept of their distance from it. This helps cranes avoid smacking into the wire. 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 #14 (OR #15). 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 24, 2001. Copyright 2001 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form