Whooping Crane Migration Update: April 10, 2001 Today's Report Includes: Whoopers Confirmed Over Nebraska! Tom Stehn Reports: Cranes on Schedule Above the Clouds? Challenge Question #11 Stay or Go? Challenge Question #12 High Wire Hazards: Challenge Question # 13 Missing Sandhill Cranes: Discussion of Challenge Question #10 Whoopers Confirmed Over Nebraska! Migration Route Map by Claudia Fonkert Macalester College Wally Jobman, wildlife biologist on Nebraska's Platte River, just reported this exciting news: "Seven whooping cranes were observed flying north from Harlan County Reservoir, Harlan County, Nebraska, at 11:30 am on Sunday April 8. A State Conservation Officer confirmed that they were whooping cranes." Last week Wally said a storm center was moving through Kansas and Nebraska on Friday, April 6, but the weekend would likely bring nice days. As a result, Wally said, "I would expect many of the sandhill cranes along the Platte River to leave this weekend, and whooping cranes should also be migrating into the area." Now let's hear what Tom Crane found on his most recent flight (April 4) over Aransas. Tom Stehn Reports: Cranes on Schedule Dear Journey North, This time I'm sure some of the whooping cranes have started the migration. During a census flight I did April 4th, I could only find 140 whooping cranes. Nine adult pairs were not found on their territories, a pretty sure sign they have left for the winter. I estimate that as many as 34 of the total of 174 in the flock have headed north. The majority of departures normally occur between April 4-12, so the whooping cranes seem right on schedule. Warmer temperatures are starting to spread throughout the Midwest, and it is time for the cranes to make their 2500-mile journey up to the Northwest Territories of Canada. Think about what conditions the whooping cranes need to make their migration easier. If you know these conditions, then you should be able to tell me if whooping cranes ever fly up through a thick cloud layer and migrate above the clouds. What would the advantages and disadvantages be? I'll give you my answer next week. Challenge Question #11 "Do whooping cranes ever migrate above the clouds? If so, what would be the advantages and disadvantages of flying above the clouds?" (To respond to this question, please follow the instructions below.) On my aerial flight, an oil slick about 1-1/4 acres in size was observed adjacent to the Victoria Barge Canal in the crane area. The slick could have come from a vessel pumping its bilges. The slick was reported to the Texas General Land oil spill response office in Port Lavaca, Texas, but by the time they got there no trace was found. That was not surprising since what I saw from the airplane was a very light, thin sheen of oil discoloring the water. Fortunately, winds were pushing the pollution away from the crane marshes. I do worry about what a major chemical spill could do to the whooping crane habitat. But experts feel the chance of this is remote since chemicals are not unloaded or loaded onto ships or barges near whooping crane habitat. We do keep oil spill booms on the refuge to try to contain a spill if one occurs. Unfortunately, the boat traffic goes so close to the cranes that a spill could enter crane marshes before we would have a chance to respond. It is just another danger that a very endangered species continues to face as it fights to survive. Unfortunately, many species of endangered wildlife face similar threats as development and loss of wildlife habitat continues in this country and around the world. I'm going to give the remaining whooping cranes two weeks to get on out of here. I won't fly again until April 17th to see what stragglers are left. I expect to find fewer than 50 birds remaining at that time. Tom Stehn, Whooping Crane Coordinator U.S. Fish and Wildlife Service Aransas NWR Read Tom's full letter for more about departure conditions at Aransas. Find out when the Mustang Lake pair left. What happened on days with strong southeast winds and partly cloudy skies? Link to Tom Stehn's full report Stay or Go? Meanwhile, imagine you're one of the remaining whooping cranes at Aransas. What are your thoughts for the question Tom wonders about? Challenge Question #12 "Why would some of the whooping cranes be less eager than others to leave the wintering grounds?" (To respond to this question, please follow the instructions below.) High Wire Hazards Tom mentioned oil spills as one hazard faced by the cranes, with Aransas is doing everything possible to be prepared. Here's another human-caused hazard: the cellular towers springing up like mushrooms across the U.S. The USFWS has made recommendations in order to minimize the number of migratory birds killed as a result these towers. One recommendation is that the towers be kept below heights of 200 feet to eliminate the need for lighting that attracts migratory birds. Another is that towers be built without guy wires. Because the birds cannot see the wires, they collide with them and are hurt or killed. It helps if existing guy wires are marked, and many people are working on that. Lillian Annette Rowe Sanctuary on the Platte River, where thousands of migrating birds stop during migration, is a good example. They took the lead in raising money to put special little devices called Bird Flight Diverters (BFDs) on the wires. BFDs are small, simple coils. When placed every 2 meters along a wire, they somehow help the cranes to notice the wires before bonking into them. The BFDs are inexpensive, but the Sanctuary needed to raise thousands of dollars because power company crews had to use a lot of equipment and people to actually put them on the wires. They finished the job in fall 2000, so this will be the first "wire-safe" spring migration since the power lines were built. Let's hope for smoother sailing for the cranes! Challenge Question #13 "Why do you think cranes have difficulties seeing wires? How do you think little coils help solve the problem?" (To respond to this question, please follow the instructions below.) Missing Sandhill Cranes: Discussion of Challenge Question #10 Last time we gave you the latitude and longitude with this question: "If they flew 6 hours a day, approximately what date would the sandhill cranes arrive at Necedah National Wildlife Refuge in Wisconsin? What are some natural causes that might keep them from migrating for a day or two?" The distance between the Chassahowitzka National Wildlife Refuge in central Florida (Crystal River, FL at 28.9 N, 82.59 W) and the Necedah National Wildlife Refuge (44.02 N, 90.07 W) is 1122 miles (1805 km). Forty mph is the average speed that cranes fly, so if they fly 6 hours a day, they could cover 240 miles each day. At this rate, it would take them 4.675 days to reach Necedah. If the cranes left February 25 and went directly there, they would have arrived in Wisconsin on March 1. Natural causes that could hold them back during migration include:Bad weather for migrating. Food shortages. If they were leaving Florida without the fat store they normally should have, they might not be able to cover much ground each day. Unusually GOOD conditions in one spot. A good place to fatten up might just detain them for a while. Discovering a flock of cranes that are staying in an area. The cranes might just join the other cranes for a while. 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 #11 (OR #12 OR #13). 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 17, 2001. Copyright 2001 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form