Nebraskaland

66 Nebraskaland • May 2020 MIXED BAG For years, it was advertised that there were about 500,000 sandhill crane on the Platte River in Nebraska during the peak of the spring migration. More recently, the estimate was bumped up to 650,000. New research has found the number to be considerably higher – more than one million in fact. On the heels of another project that looked at the timing of the peak of the migration, Andrew Caven, director of research for the Crane Trust, started crunching the numbers provided by four different aerial surveys to find a better estimate. The U.S. Fish and Wildlife Service has been conducting aerial surveys of sandhill cranes in Nebraska since 1957. Since 1982, it has counted cranes on the river and in fields and meadows within 6 miles of the river on the fourth Tuesday in March. The problem with that survey, however, was that it didn't always take place during the peak of the migration, and in recent years varied from 400,000 to nearly 1 million, a shift that is not biologically feasible. The Crane Trust has been surveying cranes since 1982 on the Central Platte and in adjacent fields from mid-February to mid-April. That survey also has its faults, due to the number of birds that leave the river prior to the morning flight. It did, however, show that the migration peaked anywhere between March 8 and April 8, including 2019, when its peak found 660,000 cranes on the river. A third study from 2000 to 2003 used thermal imaging surveys to count cranes roosting on the river at night in late March, finding about 500,000 cranes on the Central Platte, believed to be the most accurate count for a given time. In the fourth survey by the Rainwater Basin Joint Venture and Fish and Wildlife Service, researchers counted cranes on the North Platte River between North Platte and the Wyoming line and the South Platte River between North Plate and Hershey. "We tried to use all of these different studies to correct the biases in each of them and increase the coverage and come up with an overall estimate of how many sandhill cranes there are in Nebraska at the peak of the migration," Caven said. "That led us to a center point estimate for 2018 of about 1.27 million birds, with 220,000 in the North Platte River Valley and 1.05 million in the Central Platte River Valley." Doubling the estimate in the Central Platte in 20 years is feasible considering an accepted annual population growth rate of 3.7 percent. And considering that some cranes arrive in Nebraska and leave earlier than others, Caven's study estimates that on a given year, there may be a peak of between 1.1 and 1.4 million cranes in Nebraska at one time, and there are believed to be 1.5 million birds total in the mid- continent population. Estimates won't be available for 2020: the Covid 19 pandemic grounded planes for the Fish and Wildlife Service surveys. Caven said based on his surveys, which counted both fewer cranes than last year and a prolonged peak, the overall peak would have been lower this year. MORE THAN 1 MILLION CRANES IN NEBRASKA By Eric Fowler PHOTO BY ERIC FOWLER

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