Con: Expert vouches for longtime method of counting whooping cranes
By Dianna Wray - DWRAY@VICAD.COM
March 3, 2013 at 10:05 p.m.
Updated March 3, 2013 at 9:04 p.m.
The old method was more accurate, according to the expert who counted whooping cranes for three decades.
"I'm totally against the new approach. I'm an old-fashioned dinosaur, but sometimes you've just got to realize that the old way is better than the new way," said Tom Stehn, former whooping crane coordinator.
Stehn started conducting an annual census of the whooping cranes when he started his job as whooping crane coordinator in 1982.
He learned his method of surveying the whooper population from the pilot who flew with the previous biologist.
The new method of surveying provides an estimate of the size of the flock after going over a set area counting the birds and then calculating the birds that will be wintering in other areas that have not been flown over.
Stehn's method divided the known crane wintering areas on a grid, and the pilot would fly over the sections until 100 percent of the area was covered.
Stehn had to rely on hand-drawn sketches of the marshes, but he learned the areas over time and eventually acquired aerial photos and then a GPS system that ensured they were covering the entire whooping crane territory during their surveys.
"It's the traditional method that's been used dating back to the 1950s. I just continued it," Stehn said. "I refined it and got better and better over time."
Jim Blackburn is a Houston-based environmental lawyer representing the Aransas Project in a lawsuit against the state over the deaths of 23 whooping cranes in the 2008-09 winter season.
In the trial, Blackburn argued that the Guadalupe-Blanco River Authority did not allow enough water to flow to the bays during that dry season, causing the deaths of the birds. The numbers were taken from Stehn's survey where he recorded the deaths of 23 birds.
Stehn was whooping crane coordinator for the U.S. Fish and Wildlife Service from 1982 to 2011. He conducted his surveys by flying a plane over the Aransas National Wildlife Refuge and the grounds nearby where he knew whooping cranes spent their winter months.
Blackburn said he opposes changing the counting method because wildlife officials provide only estimates instead of a solid number of birds in the flock.
"To try to keep track of the head count and the losses is incredibly important," he said, noting that this is how they record births and deaths within the flock.
The change in the survey method from a direct census to an estimate could make it harder to track a sudden increase in deaths that might be linked to environmental problems, he said.
"I'm not convinced the new methodology is the best option," Blackburn said. "I'd like to see them look at a way to do surveys that will better calculate mortality."
Stehn was grilled in the trial over the deaths he reported as the defense attorneys asked how he could be sure that the birds were dead.
After 29 years working with the birds and studying their habits and movements, Stehn testified that he knew the birds well enough to know that whoopers rarely leave their family units, and if a bird disappeared, it was because the bird had died.
Stehn said he was usually about 98 percent certain of his counts of the whoopers.
The new survey method, with a 95 percent confidence interval ranging between 178 and 362 birds in the flock, doesn't provide enough accuracy to detect smaller increases and decreases in the flock, he said.
Stehn noted that these smaller changes are important to track in a flock this size because they can be correlated to changes in salinity in the bays, conditions in the Canadian marshes, the number of blue crabs or a variety of other factors that could impact the flock's growth.
"The current method is just not sensitive enough to these changes. End of story," he said.
Chester McConnell, a longtime member of the Whooping Crane Conservation Association, noted he and other members try to support the U.S. Fish and Wildlife Service and to work with them. However, he said he and other members of the association had hoped someone would be brought in and given the chance to learn from Stehn so the new person could continue using his method of counting the whoopers.
"These types of statistical analysis were developed for populations of animals or plants that have thousands and thousands in their population. When you try to apply that method with a small population, you have those very wide intervals," McConnell said.
Wade Harrell, the whooping crane coordinator who replaced Stehn, said no one has enough experience to replicate Stehn's census methods. Stehn disagreed, saying he believes someone trained in bird identification could conduct a census that would be more accurate than the survey estimate after six or 12 flights.
"What frustrates me is that they haven't even tried my method," he said. "In all my years of doing it, no one ever questioned it."