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ZIMS at Work: How Texas zoos returned this species to its natural habitat

Houston, TX – Matt Lammers and his coworkers with the Houston Zoo were long-awaiting rain at Griffith League Scout Ranch in Bastrop County, Texas when, on a day in early August of this year, it finally came. Knowing the opportunity would not last long, they loaded their precious cargo and drove out to a small pond on the ranch and set to work removing miniscule amphibious eggs from five-gallon buckets and gently placing them in protective enclosures in the shallow water.

For Lammers, this was a critical step in saving a species that had once thrived in the region. As coordinator of the Houston Toad Recovery Program he and his coworkers were on a mission to save one of southern Texas’ most iconic amphibians from the brink of extinction.

Anaxyrus houstonensis released into Griffith League Scout Ranch. The sandy soil beneath a mixed pine and deciduous forest is a favorite habitat for the Houston toad. Credit: Houston Zoo

Decades ago, the amphibian species Anaxyrus houstonensis, better known as the Houston toad, could be found throughout southeast Texas, with Bastrop County as the far-western border of the toad’s habitat. The sandy-soiled forests it called home rang with the species’ characteristic high-pitched trills, and during breeding season tadpoles would throng about innumerable small ponds and nearby grasslands.

Nowadays, the population in Bastrop County makes up one of just a few isolated populations of the small toad scattered through their former range. According to surveys by the Texas Parks and Wildlife Department and Texas State University between 2000-2007, the Houston toad – found nowhere else in the world – would soon be extinct. But a massive breeding and wild-release project called the Houston Toad Recovery Program, led by Association of Zoos and Aquariums (AZA) member the Houston Zoo in partnership with the Texas Parks and Wildlife Department, Texas State University, Fort Worth Zoo, Dallas Zoo, USFWS Fish Hatchery and private landowners, is giving these unique animals a fighting chance at survival.

Stan Mays, curator of Herpetology and Entomology at the Houston Zoo and Conservation Liaison for the Houston toads, spoke at length with Species360 to illustrate the Recovery Program’s approach to conservation.

“Ultimately our role is to produce as many eggs and get them out into the wild as quick as possible and get the wild populations reestablished,” Mays said.

A Toad in Need

            The Houston toad is a brownish speckled amphibian more closely related to the wide-ranging American toad than the hardy Gulf-Coast toad it often shares territory with. While it was named for the small area the species occupied around the largest city in Texas, there hasn’t been a Houston toad seen in the city since the late-1970s. The toad is remarkable in its high-pitched song, the very specific habitat in which it thrives, and the fact that in 1970 Anaxyrus houstonensis was the first amphibianever added to the federal list of endangered species.

A worker with the Houston Toad Recovery Program releases toad eggs into protective enclosures at Griffith League Boy Scout Ranch. The wire enclosures offer protection during the toads’ vulnerable hatching stage. Credit: Houston Zoo

Despite its early identification as a species in need, the Houston Toad was only formally recognized as a new species in 1953. Since the very beginning of its discovery by the scientific community, this humble toad has been struggling to survive in the face of relentless human encroachment and destruction of its natural habitat. The ponds and forests wherein it once lived have been demolished and the remaining toad populations fragmented.

A sad example of that fact: The supposed location where one of the first Houston toads were found in Katy, Texas was drained and paved. The site of that pond, Stan Mays quipped, is now covered by a shopping mall parking lot,” Mays lamented. “It’s the rapid urbanization… it’s just such a huge loss.”

Ultimately, the ongoing degradation of Houston toad habitat led the species to have small, isolated populations unable to weather larger environmental disasters. The precarious situation reached a climax in 2010, when southeast Texas suffered a terrible drought. The following two years saw fires engulf the pine and oak forests that cover the region, nearly eliminating the Houston toad entirely. Years of improper forest management resulted in a thick layer of brittle debris covering the traditionally sandy soil. Once, the toads could survive forest fires by burrowing into the sand, but this time the forest floor itself burned, and the there was nowhere for the toads to go to escape the ensuing inferno.

The loss was devastating, and not only for the Houston toad. Already, the wildlife in southeast Texas was slowly, yet noticeably, shrinking back into small pockets of wilderness.

Breed and Release

The Houston Toad Recovery Program has been going on for a while. “We first started in the Houston Toad program in 1978,” Mays said. “The first few years were just trying to learn how to keep them alive in captivity.”

In 2007 the Houston Zoo renewed its recovery work with a new goal; to breed toads for release into the wild and to establish a captive assurance colony in case disaster struck. Zookeepers with Houston Zoo capture toads and breed them, then release the fertilized eggs into designated protected areas safe from human development. Specially developed hormone treatments are used to time the breeding season with the ideal release season in the wild, typically from mid-February through May.

Tanks used to house young toads for release and addition to the assurance colony in one of several biosecure breeding and housing rooms. Houston Zoo’s adult toads that make up the assurance colony are housed in similar fashion. Credit: Houston Zoo
Houston Toad egg strands in a breeding tank. The breeding season for captive Houston toads is closely regulated using hormonal treatments. Credit: Houston Zoo
A close-up of Houston toad egg strands. Houston toads bred in the recovery program average 7,200 eggs per strand, though they have been known to lay as many as 15,000 eggs. Credit: Houston Zoo

Since Houston Zoo spearheaded the assurance population and reintroduction program, a strong partnership has formed between the Texas Parks and Wildlife Department, private landowners including the Boy Scouts of America who are eager to provide spaces for the toads to flourish, fellow zoological institutions that expand the reach and scope of the recovery effort, and Texas State University biologists, which handle field work for the program.

In 2013, Houston Zoo released its first group of over 36,000 toad eggs to the wild. Since then, the program has exploded in size and scope. This year alone, Houston Zoo and its partners released over 800,000 toad eggs, juveniles and tadpoles. Over the course of the program, they have released over 6.3 million.

The success of the program has been remarkable. Houston toads are still rare throughout southeast Texas, but thanks to the recovery program’s efforts Houston toads can once again be heard in many ponds and forests near the program release sites. While there is no way to accurately estimate the number of toads in the wild, the chorus of toads calling in Griffith League Ranch suggests that the population has risen to pre-1980s levels there. The toads are spreading even faster than initially thought possible. In one incident just a few years ago, a Texas State University team discovered that a small population of toads – descendants of a group released in the 1980s – had migrated almost 35 miles upstream along the San Bernard River.

“We had no idea that these things moved like that. [The toads] are always teaching us something new,” Mays said. “We’re always learning something new from them and adapting our methods as we learn.”

Contributing Data Essential to Conservation

            In coordinating with multiple zoos and wildlife institutions across Texas, data management and information sharing capabilities are integral to the long-term success of the Houston toad recovery effort. As a member of the global nonprofit Species360, the Houston Zoo uses the Zoological Information Management System (ZIMS) to curate and share information about the Houston Toad and hundreds of other species.

In his role as studbook keeper for the Houston toad, Stan Mays tracks the genetic diversity of the assurance population and helps determine which egg strands will be bred for future toad reintroductions. He uses ZIMS for Studbooks to manage his breeding groups.

“To me the main thing is convenience,” he said, describing how easy it is to share information with his counterparts in the ZIMS network.

The Houston toads also benefit from data-driven medical attention thanks to ZIMS for Medical. Dr. Maryanne Tocidlowski, the head staff veterinarian for the Houston toads, can examine the health of individual toads or analyze the entire population of over 500 toads in the assurance population.

“Our adult toads get an individual ID number thus each have a separate medical record.  Our younger toads are in group numbers. I use ZIMs often when there is a toad medical case, and these are treated just like any other animal,” she said.

As a non-profit dedicated to empowering zoos, aquariums and wildlife conservation organizations, Species360 is proud of our role in helping Houston Zoo and our other member institutions in their conservation efforts around the world. The Houston Toad Recovery Program embodies the Species360 mission of using data and cooperation to protect and conserve species.

As Stan Mays says, “[The recovery program] is showing what a bunch of people can do together if they all agree on the central concept, which is preserving the Houston Toad.”

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