September 13, 2011 | 1
Devastating fires that swept through eastern Texas this month have left dozens of people dead or missing and destroyed more than 1,500 homes. The fires have also dealt a horrible blow the endangered Houston toad (Bufo houstonensis), which had already been suffering due to years of drought that preceded the flames.
Houston toads started disappearing from much of their historic range (including the city the species is named after) decades ago, as habitat loss forced them into smaller and smaller territories. The toads now only exist in a few small populations, the largest and only genetically viable of which was located in the 2,400-hectare Bastrop State Park, more than 98 percent which was burned in the latest wildfires.
Prior to the fires, researchers estimated that maybe 500 adult toads remained in the wild, 200 of which were in Bastrop State Park. The future of that population is now in question. “Bastrop, the only place we know the population was big enough to survive, has just been lost,” says Michael Forstner, a biologist at Texas State University–San Marcos, who has spent years studying the Houston toad. “The worst part is Bastrop was the place that if we lost them everywhere else, we thought we could hold them there.” Forstner says that tests on other populations show they are as genetically similar as sibling groups.
According to the Houston Toad Recovery Program, managed by the Houston Zoo, only 10 to 15 Houston toads were observed across their nine-county range in 2011. Many of those observations were made aurally, when the male frogs were chorusing for mates, so females or juveniles went uncounted. Visual observations are difficult, as the tiny toads are just five to nine centimeters across, heavily camouflaged, and spend much of the year underground hiding from the Texas heat.
That last characteristic may have saved many of the Bastrop toads. “They were likely to have been deep enough in the ground that the fire did not impact them,” Forstner says.
While the toads may or may not have survived the fires, it’s the coming months that will truly test the population. “What happens when they come out of the ground this fall, late this winter or spring, when or if it rains again?” Forstner asks. All of the herbaceous growth in the park has been burned away, taking with it the insects the toads eat and the cover they rely on for safety.
If the drought continues, male toads will probably have to travel great distances to find mates, if they can find them at all. “Should you have a successful chorus and mating, the emergence of juveniles will have the same problems” finding food and shelter, Forstner says. It also doesn’t help that female toads prefer large choruses, indicating a large number of mates, and tend to avoid choruses of just a few individuals.
The final fate of the toads in Bastrop won’t be known for months. “The verdict isn’t in,” says Andrew Gluesenkamp, herpetologist with the Texas Parks and Wildlife Department. “We’re going to know a lot more about the status of the species and the obstacles toward recovery in a few months. Right now, we’re crossing our fingers and hoping for the best.”
One source of hope for the Houston toad is a captive assurance program maintained by the Houston Zoo, which now has at least 2,500 toads representing about 21 different genetic lines, significantly more toads than are estimated to live in the wild. “One of the primary reasons we brought toads into captivity in 2007 was insurance against catastrophic events,” says Paul Crump, the zoo’s amphibian conservation projects manager. “It’s absolutely horrendous that it’s actually happened.”