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When a group of researchers at Texas A&M’s Natural Resources Institute published the first peer-reviewed study that surveyed the presence of a brightly colored Texas songbird across a huge swath of Texas, the results were astounding: The population of the endangered golden-cheeked warbler in the state was estimated to be 10 times larger than previously thought.
The 2012 study did not advocate changing the species’ endangered status, nor did it imply that conservation measures to protect its habitat were no longer necessary, researchers said at the time.
“Rather,” said Heather Mathewson, the lead researcher, “this study is one of many necessary steps in our evolving knowledge of the golden-cheeked warbler.”
“[It] is not intended as the final word on the matter,” she added.
Nonetheless, the data point — without indicating whether the warbler’s population was increasing or decreasing in Texas — has fueled an almost decadelong legal battle over the bird with a bright yellow face and striking black marks. In 2015, the Texas Public Policy Foundation and Susan Combs, a Republican state leader who had served as Texas’ comptroller, its commissioner of agriculture and a state representative, petitioned the federal government to remove the warbler from the endangered species list. The petition used Mathewson’s study as primary evidence that the bird no longer needed such stringent federal protections.
“The time has come to remove the golden-cheeked warbler from the endangered species list,” the petitioners argued. “Delisting this species is now compelled by today’s best available science.”
The latest lawsuit to remove the bird from the endangered species list was filed last week, part of a heated legal battle for which the 2012 study and its fundamental research question — how many golden-cheeked warblers exist in Texas? — have become a lightning rod. The ongoing fight comes as Central Texas faces enormous demand for new housing developments as the state’s population surges.
The federal government, in rejecting attempts to delist the bird, attacked the research methods of the biologists. Meanwhile, the TPPF — and eventually, the Texas General Land Office — characterized the study’s findings beyond what they actually suggested, arguing that the bird’s population had recovered and did not face any current significant threats.
“This really shouldn’t be controversial,” said Michael Morrison, a professor of wildlife and fisheries sciences at Texas A&M and one of the wildlife biologists who worked on the 2012 study. “You would think we should be celebrating the fact that … the bird is far better off than we thought.”
The federal government typically places the population of male warblers at about 27,000, based on a 2007 estimate by SWCA Environmental Consultants for the Texas Department of Transportation. Mathewson and her colleagues estimated the actual number is closer to 263,000. In a five-year review of the bird’s status published in 2014, the Fish and Wildlife Service wrote that the differing estimates underscored the need for more information.
A separate assessment of the bird’s population conducted in 2018 by Jim Mueller, a U.S. Fish and Wildlife Service scientist, estimated that there may be about 233,000 male warblers in Texas; those results are still undergoing peer review for publication in a journal, he wrote in an email to The Texas Tribune.
“The current population size is much larger than was estimated,” Mueller said in a comment. “That is fantastic news.”
“On the flip side, threats to the species continue, such as loss of habitat,” he said.
Human habitat encroaching on warbler country
The golden-cheeked warbler’s habitat ranges across a 35-county region of Central Texas from west of San Antonio up to the Dallas-Fort Worth metropolitan area. It follows and expands northwest of the Interstate 35 corridor, a rapidly growing region of Texas where the population of humans grew by 50% between 1990 and 2010. The bird was first listed as endangered in 1990; the primary considerations were the rapid decline of habitat and its small estimated population size.
The migratory songbird breeds in Texas between late February and the end of April before heading south to Central America in the late summer. Its breeding range extends across 67,000 square kilometers, or roughly 25,900 square miles, of Texas, Mueller said. But, only about 4% of that area is suitable woodland habitat since the bird relies on Ashe juniper bark to nest, he added.
The federal government has previously rejected Texas’ attempts to delist the bird based on new population estimates alone. The U.S. Fish and Wildlife Service argues that there isn’t evidence to suggest threats to the bird’s existence have been reduced. In fact, the opposite has been found: Destruction of the bird’s habitat has only accelerated across Central Texas as suburbs expand around San Antonio, Austin and Dallas. One 2013 study found that between 2001 and 2011, the golden-cheeked warbler’s habitat shrunk by 29%. Scientists have found that the primary drivers of its habitat loss are rapid suburban development outside of Austin and San Antonio.
The Texas General Land Office manages state-owned lands and mineral rights totaling 13 million acres, according to the agency. After the federal government rejected its first attempt to delist the bird, the Texas General Land Office joined a 2017 lawsuit to delist the bird by the TPPF, arguing that the agency leases lands to benefit the Permanent School Fund, and endangered species restrictions lowered property values.
On appeal, a 5th U.S. Circuit Court of Appeals judge in 2020 ordered the Fish and Wildlife Service to reconsider Texas’ petition, stating that the federal agency had used an incorrect legal standard to evaluate whether the bird’s endangered status should be reconsidered. The federal agency issued another finding in July, again rejecting the attempt to begin a process that could delist the bird.
“These efforts represent new estimates rather than indicators of positive trends in warbler habitat and population size, and thus do not imply recovery,” the Fish and Wildlife Service wrote of the 2012 population study.
But Ted Hadzi-Antich, a senior attorney with the Texas Public Policy Foundation and lead counsel on the warbler case, argues to the contrary.
“To my mind, it’s pretty clear that [the population] is increasing, and that the habitat fragmentation, predation and urbanization have not been adversely impacting the warblers,” he said.
Hadzi-Antich said that the state’s General Land Office is likely the single most-impacted entity by the continued listing of the golden-cheeked warbler. For example, he said about 85% of a 2,300-acre parcel of land between Bexar and Kendall counties is considered warbler habitat; GLO estimated that the endangered species protections on that site have decreased its property value by 35%.
“They wanted to develop that property, but with this diminution in value, that became problematic,” he said. “Nobody wants to see species become extinct. The problem is, you’ve got palpable adverse impacts on humans from some of these requirements.”
“The [Endangered Species Act] is intended to protect species from extinction, not protect species from the supposition that there may be a threat,” he added.
George P. Bush, the Texas land commissioner and a candidate for Texas attorney general, has long fought against Endangered Species Act protections that block urban development. In 2015, he led an alliance of state land commissioners challenging how species are listed. On Wednesday, Texas and the TPPF sued the U.S. Fish and Wildlife Service again, arguing that the federal government refused to abide by the judge’s instructions.
In a statement, a spokesperson for the Fish and Wildlife Service said the agency does not comment on pending litigation.
Conservation advocates, meanwhile, generally agree with the federal government that the threats still exist to the warbler’s population.
“Scientists from around the world are ringing the alarm bells that we’re in an extinction crisis,” said Noah Greenwald, the endangered species director at the Center for Biological Diversity, a nonprofit advocacy group. “The golden-cheeked warbler challenges us to protect woodlands in an area that’s being rapidly developed.”
Erin Zwiener, a Democratic state representative who has advocated for conservation of natural areas and represents House District 45, west of Austin — which includes a large swath that serves as habitat for the golden-cheeked warbler — said the increased costs to developers from the endangered species protections don’t entirely block growth, and the current rules help to protect natural areas in the Texas Hill Country.
“Warbler habitat is largely in some of the most desirable places to build in the state,” Zwiener said. “We are still experiencing rapid growth despite the protections.”
“Honestly, I don’t know many people around here who would complain about development being slightly slower,” she added.
Science caught in the middle
Evolving science — better surveys, better models, more testing — provided the ammunition for the hotly contested legal battle over the development of Central Texas. Morrison, the biologist who worked on the 2012 study, said he’s frustrated by the way researchers and the science supporting their findings have been characterized along the way.
“We’ve been accused by environmentalists that somehow, we as the scientists want [the warbler] to not be [on the] endangered [list],” Morrison said.
The Fish and Wildlife Service sought in part to discredit Morrison and his colleagues, arguing that the estimate of land occupied by the birds used in the study was not reliable and that it may have led to an inflated estimate of the total population. But Roel Lopez, director of Texas A&M’s Natural Resources Institute, said that researchers used robust methodology, the most current technology available and random sampling to determine potential habitat and the population estimate.
“The methods back then [in 1990, when the warbler was first listed as endangered] may not have been as robust, or there wasn’t a lot of information,” Lopez said. “Through time, there may be an increased effort to survey and sample more, so it’s not uncommon for us to work on a species and — through an increase in effort — actually find more of them.”
On the other hand, the assertion by the TPPF that the bird’s population has ballooned since 1990 is very unlikely and not supported by research, experts said. Scientists may never know how many birds there were in 1990 or how much the population has declined since then.
But Morrison said that misses the larger problem, which is how to ensure enough warbler habitat remains in Texas Hill Country.
“We need to be focusing on working with landowners to maintain large continuous tracts of habitat, give them tax breaks, and reasons to maintain that,” Morrison said. “Fighting over whether or not there’s 100,000 or 200,000 [male birds], to me, is kind of not the point.”
Disclosure: Texas A&M University, the Texas General Land Office and the Texas Public Policy Foundation have been financial supporters of The Texas Tribune, a nonprofit, nonpartisan news organization that is funded in part by donations from members, foundations and corporate sponsors. Financial supporters play no role in the Tribune's journalism. Find a complete list of them here.