AUSTIN, Texas (AP) — The population of golden-cheeked warblers, among the most famed of endangered species in Central Texas, is higher than previously estimated, according to research by Texas A&M University scientists to be published later this summer.
The researchers calculate the rangewide population of male warblers in Texas at a shade over 263,000. Previous surveys counted roughly 9,000 to 54,000 birds. The work will be published in the Journal of Wildlife Management; it was posted on the journal’s website earlier this year.
The new figure comes as the U.S. Fish and Wildlife Service conducts a five-year review of the warbler.
The small bird, characterized by the male’s yellow cheeks outlined in black, was one of several species at the heart of battles between developers and environmentalists in western Travis County in the 1990s.
So striking is the new figure that David Wolfe, Texas regional wildlife director for the Environmental Defense Fund, said in an interview that the species would “probably not” have been listed as endangered in 1990 had the Fish and Wildlife Service had these figures then.
The delisting of species is uncommon.
In the past several years, only one species has been delisted in the region that includes Texas. The region has 136 listed endangered species, said Tom Buckley, a Fish and Wildlife Service spokesman.
Why the variation in population estimates?
The A&M researchers expanded the potential warbler breeding area to 35 counties, much of it land that previous researchers had either waved off as unlikely warbler territory or that researchers could not access because it was private property. For their work, the A&M researchers gained the cooperation of landowners with the use of confidentiality agreements.
“Our study was the first one to look at the entire breeding range,” said Michael Morrison, a professor of ecology management and one of the study’s authors. Previous work had assumed “that the bird did not occur in a lot of areas in high densities,” he said. “We went there and found them.”
It’s unlikely that the population simply jumped from the earlier studies, some of which were done more than 30 years ago, and now, Morrison said.
“Nobody knows whether the birds were there when the species was listed, but you can pretty well assume it was higher than previously thought,” he said. “Nobody is going to say the population has gone up that much.”
The report does not advocate changes in the listing status of the golden-cheeked warbler nor does it imply that conservation measures to protect the species habitat are no longer needed.
As part of a compromise plan to allow development in parts of warbler-rich western Travis County, the City of Austin and Travis County agreed to piece together and manage a preserve of roughly 30,000 acres. (The LCRA also plays a small role.) The preserve land, which also benefits other endangered species, is paid for, in part, with development fees.
The study did pass through a peer review process, but Willy Conrad, manager of the wildlife conservation division at the Austin Water Utility, sounded a skeptical note about the A&M findings. The sampling method used by the researchers, which involved two observers tracking the singing male birds, has been known to “grossly overestimate populations” because it could lead to double counts, he said.
Even if the warbler were delisted, Conrad said, the city and county probably would continue to manage the preserve. He said the preserve has “contributed to the recovery of the species.”
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Information from: Austin American-Statesman, http://www.statesman.com
