Las Vegas Sun

August 24, 2019

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Local biologists try to reintroduce a rare frog species into Southern Nevada


Steve Marcus / Relict leopard frog (R. Grayson & Aaron Ambos/Springs Preserve/Courtesy)

Despite the arid desert climate, the relict leopard frog once thrived in the region before the growth of Las Vegas changed its habitat. During the 1950s, it became what was thought to be the first extinct amphibian in North America, according to the Center for Biological Diversity, until it was spotted again in the early ’90s.

Quick facts:

■ Size: 1 3/4 – 3 1/2 inches long

■ Markings: Primarily brown, gray or green with greenish brown “leopard spots”

■ Habitat: Lowland streams, springs and wetlands surrounded by deserts

■ Officials believe there were only 500-1,000 adult frogs remaining as of 2015.

More recently, biologists at the Springs Preserve have introduced dozens of the spotted frogs to a new habitat constructed along the historic Las Vegas Creek channel.

They hope the controlled location will give the frogs an increased chance of survival.

“Keeping the species alive is part of keeping the ecosystem intact,” says Raymond Saumure, an environmental biologist for the Southern Nevada Water Authority.

Near extinction

What do they eat?

Relict leopard frogs “eat just about everything that moves,” Saumure said. These include snails, spiders and insects. Tadpoles feed on algae and other plants. They also eat a large variety of small aquatic microorganisms and dead insects.

Relict leopard frogs have historically inhabited areas along the Virgin and Colorado rivers, along with a scattering of springs around the Southwest, according to the Center for Biological Diversity.

In 2002, the Southern Utah Wilderness Alliance filed a petition with the U.S. Fish and Wildlife Service to list the species under the Endangered Species Act. Instead of receiving endangered status, the frog was designated as a candidate for federal listing. State and federal agencies have since drafted a conservation agreement strategy, and reintroduction projects were launched in six springs in Arizona and Utah in 2006.

The species is considered vulnerable today.

Biological invaders

Invasive species are a major threat to relict leopard frogs and include the following:

• Tamarisk: Invasive vegetation can grow and make areas too dense for the frogs to thrive, choking out open banks and deep pools.

• Western mosquitofish: Originally introduced to control mosquitoes, the western mosquitofish is considered extremely aggressive and consume smaller fish, eggs and tadpoles.

• Red swamp crayfish: Also known as the Louisiana crawfish, this species is known to prey on native fish. Their feeding behavior also reduces habitat for amphibians. Native to the Gulf Coast of the Mississippi River, they were likely spread in other waters when released as former study specimens and pets.

• Bullfrogs: The bullfrog is the largest species of frog in the United States, with males reaching up to eight inches. They are native to North America, east of the Rocky Mountains but were introduced by early settlers in the West as a food source because of their size. They eat just about anything, including smaller frogs, Saumure said.

Ideal habitat

Relict leopard frogs are “habitat generalists,” meaning they can occupy a variety of landscapes, including streams, springs and wetlands. Saumure said the optimal habitat provides open water and vegetation where frogs can hide and sun themselves.

Observations from studies suggest that adults prefer open shorelines (without dominant vegetation), pools and streams with continuous water flow year-round for tadpole development, and some vegetation within pools on which egg clusters can attach.

They are often found in geothermal springs with temperatures 86 degrees and above.

While the habitat at Springs Preserve isn’t heated, Saumure said the frogs are still successfully breeding at a faster rate than expected and the froglets released in May have already produced tadpoles. A mating pair can produce 600.

“The experiment was to see if they could survive in an environment like this,” Saumure said.

The ponds were built near native vegetation and stocked with relict leopard frogs and the endangered Pahrump poolfish. Visitors to Springs Preserve have access to the site via trail.

The biggest challenge in creating habitats for the frogs is the “unknown”—there is still so much to learn about the species, Saumure added.