Whooping crane flock size estimated smaller than last year
By by Dianna Wray - DWRAY@VICAD.COM
Feb. 16, 2013 at 1:04 p.m.
Updated Feb. 15, 2013 at 8:16 p.m.
ABOUT THE FLOCK
The whooping cranes begin migrating to Aransas National Wildlife Refuge by mid-October, returning to Wood Buffalo National Park in the Alberta and Northwest territories of Canada in the spring.
This is the only naturally migrating flock of whooping cranes in existence.
Whooping cranes have been migrating to Aransas National Wildlife Refuge since the ice age.
Source: Aransas National Wildlife Refuge website
After weeks of waiting, the U.S. Fish and Wildlife Service has issued its first count of the whooping crane flock using a new estimation technique.
The preliminary analysis estimates the flock to be made up of about 257 birds with a 95 percent confidence interval that ranges between 178 and 362 whoopers, according to a release issued Friday.
This is a disappointing development for longtime whooping crane enthusiasts, Chester McConnell, a trustee emeritus with the Whooping Crane Conservation Association, said.
"We watch these numbers religiously, and we were hoping the flock would reach 300 birds in the next few years, but now they're saying there are 40 less birds," McConnell said.
The counting system was changed after Tom Stehn, the whooping coordinator for 29 years, retired last year, and there was no one with Stehn's institutional knowledge to replace him, McConnell said.
"Tom became very proficient and was counting what he and we believed was a total count with five to seven flights over the territories, knowing the birds tend to stay in one place," McConnell said. "He had the type of skill and knowledge base that we could rely on his counts."
However, after Stehn retired, those who replaced him didn't have the skill or the knowledge to count the birds, leading the group to change its procedure. It now gathers enough information on survey flights to estimate the size of the flock instead of a direct head count.
When Stehn started out, the population was much lower and very easy to count from an airplane. The marsh was open, and he could see these big, white birds. Over time, he became more skillful in counting, McConnell said.
Still, he understands why the U.S. Fish and Wildlife Service chose to conduct estimates, he said.
"The new guys came in, and they're great guys, very smart, but they didn't have the skill, couldn't spot the birds, so they went to the statistical method," he said.
McConnell, a wildlife biologist who lives in Spanish Fort, Ala., has been involved with the association for years. He, along with other longtime followers of the whooping crane flock's progress, had hoped to see the flock size swell past 300 birds in the near future. The change in the counting method and the loss of Stehn's knowledge seem to have put that day off, he said.
Last year, the flock in the primary survey area around Aransas National Wildlife Refuge numbered 283 birds. This year's estimate, even with the addition of about 6 to 11 percent of the flock believed to be wintering outside the survey area, only brings the total to about 277 birds, according to the release.
Attempts to reach Wade Harrell, whooping crane coordinator for the Aransas National Wildlife Refuge, for comment were not successful.
The U.S. Fish and Wildlife Service acknowledged there is some uncertainty in its estimates, shown by its inclusion of a confidence interval indicating the possibility they could be off, and the flock could number from 178 to 362 birds, according to the release. However, it was noted that this is their first year using this new method and that the count will improve over time.
"Every year, we do this survey we will learn something new and different and apply it to the next season," according to the news release. "We expect this process will take several seasons before the obvious and not-so-obvious factors can be incorporated into the survey protocol and statistical models. This is how science progresses."
McConnell said the Whooping Crane Conservation Association has worked closely with the U.S. Fish and Wildlife Service in the past, but he and other members disagreed with changing to this new system.
The approach being employed is one traditionally used in areas where there isn't a lot of visibility and the number of birds or plants needs to be estimated. It is usually applied to larger numbers of animals or plants, making the margin for error smaller than it is when estimating the size of a few hundred birds, he said.
McConnell said he and the other members of the organization are frustrated with the change, but they had a good relationship with the U.S. Fish and Wildlife Service for years, so they're trying to be understanding.
"We try to work with them and support them. We do have differences in the new count method that U.S. Fish and Wildlife Service is using, but due to circumstances, it appears we are stuck with it," he said.