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FOR USE IN WEEKEND EDITIONS FEB. 11-12 - In this Feb. 2, 2012 photo, Donald Brown, a Biology doctoral student at Texas State University, takes weather data during a search for Houston toads at a pond near Bastrop, Texas. The tea-colored watering holes around Bastrop are the last stronghold of the endangered amphibian, which is about the size of a partially flattened apricot. But after years of drought and development, topped five months ago by searing wildfires, Texas State University biology professor Mike Forstner fears the worst.

BASTROP, Texas — Mike Forstner tromps along the mucky edge of a pond, trilling loudly as he sweeps the beam of his flashlight over the bank.

He's hoping for an answering call from an endangered Houston toad, but he hears nothing.

The tea-colored watering holes around Bastrop are the last stronghold of the endangered amphibian, which is about the size of a partially flattened apricot. But after years of drought and development, topped five months ago by searing wildfires, Forstner fears the worst.

"I believe the Houston toad effectively ceased to exist as a purely wild species on Sept. 5, 2011," said Forstner, 47, a biology professor at Texas State University who is spearheading the Houston toad recovery effort.

"We've had the most rain since 2002, and it was insignificant to motivate the Houston toad to chorus. That's not good."

A week after that late January hunt on Griffith League Scout Ranch, though, when temperatures warmed slightly, Forstner and his crews heard three of the grayish-brown toads chorusing in Bastrop County. The next night, they detected three more. Crews from the Texas Cooperative Wildlife Collection at Texas A&M University and the herpetology department of the Houston Zoo heard a few in Austin County, farther east, too.

The activity triggered a requirement that wildlife biologists inspect construction and debris removal sites inside areas that burned for toads before work can continue.

The croaking is a hopeful sign, but Forstner said long-term prospects remain grim.

Scientists monitoring the toads for the past five decades have observed a slow, steady decline in their numbers. The toads live in an increasingly fragmented habitat, their annual treks to breeding ponds bisected by roads. A fungus that affects toads and frogs and is suspected in a worldwide decline in amphibian populations might be partly to blame, too. Those forces, coupled with the drought and fires, probably have caused the collapse in population, Forstner said.

The Houston toad, the first amphibian placed on the endangered species list in 1970, is one of 10 species of toads found in Texas and the only one that lives solely in the Lone Star State. Once spread across 12 east-central Texas counties, they're now found mainly in Austin, Bastrop and Leon counties.

"It's a native species, a native Texan that needs help," said Paul Crumb, head of a captive breeding program at the Houston Zoo. "It illustrates the plight of what's going on with habitat and endangered species in the state."

The zoo has about 3,000 of the amphibians and has released more than 20,000 captive-bred toads into the wild to augment the population. Some are embedded with microchips readable by a scanner that can detect them up to a foot underground.

During breeding, the males "chorus" to draw in females, which lay gelatinous strands containing thousands of eggs. But they're finicky, chorusing only on warm, humid and still nights, usually after heavy rainfalls.

In monitoring surveys a decade and more ago, researchers detected hundreds of Houston toads in Bastrop County during breeding season. Numbers have dipped precipitously since then. After several years of finding nearly none, researchers detected 110 toads in 2010.

Last year, in the midst of drought, they recorded just eight. Three of those were on the Griffith League ranch.

Then the September wildfires burned about 40,000 acres, damaging up to 40 percent of the toads' best habitat. The blow comes on the heels of a lingering drought Forstner estimates already had killed 80 percent of the toads. The fire, he said, might have finished off half of the toads that survived the drought.

Researchers monitor the numbers in the wild through audio surveys, driving designated routes and pausing periodically to roll down the windows and listen for the toads' loud, high-pitched trill, which some compare to the sound of chirping crickets or tinkling bells. It lasts 12 to 14 seconds.

Forstner begins his surveys as night falls and wraps them up about 2 a.m. Similar surveys take place across the toads' territory, about 30 times a year during breeding season, between January and June.

When breeding does occur, tadpoles develop in a few months, crawl out of the water and scatter into the landscape, sometimes moving several miles from where they were born. As they move, they're picked off by everything from scorpions and birds to feral hogs.

"It's Normandy. They come out of the water; they hit the beach; they stay a couple of days while they transition from aquatic to terrestrial," Forstner said.

In the wild, just 1 percent of eggs survive to toadlet.

The September wildfires made those odds even worse. They depleted the toads' cover, leaving them more vulnerable to predators, which at the same time have less available food.

On a recent night, Forstner and two doctoral candidates who help with the monitoring surveys pull up at Pond 5. He rolls down the windows of his truck, kills the engine and holds up a device that measures weather conditions. He records the data: It's 56 degrees and 80 percent humidity, with winds at 1.8 miles per hour.

It's a little cooler than ideal but within the toads' window. If they're out there, they should be chirping.

He climbs out of his truck and heads to a nearby pond, as coyotes yip in the distance. He emits another trill, scanning the shoreline for toads.

Forstner listens, identifying the distant call of a spade foot toad. Leopard and cricket frogs have also been heard inside the burn zone, indicating that at least some amphibians survived the fires.

"The forest is still here. There are fragmented patches. There's a shot," he said.

Information from: Austin American-Statesman, http://www.statesman.com