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Thirty or forty years ago, on a warm spring night, an observant listener near a wetland in Grand Teton National Park might have heard a sound like a creaky door hinge or a small boat engine.

The sound was the call of a northern leopard frog, and researchers think it hasn’t been heard in the park in at least a decade. In 1995, a child visiting the park found one and showed it to a ranger. The ranger snapped a picture, marking the last definitive evidence of a rana pipiens in the region.

In a place that many wildlife enthusiasts consider the last intact ecosystem in the lower 48 states, the absence of the leopard frog in Grand Teton is conspicuous. But last week, the U.S. Fish and Wildlife Service announced that the frog could receive Endangered Species Act protection, rekindling hopes among researchers from around the region that the frog could stage a comeback.

Chuck Peterson, a professor of biological sciences at Idaho State University, said amphibian researchers documented the leopard frog at a field station near Moran Junction in Grand Teton in the early 1950s. People also reported the frog at Leigh and String lakes.

“They weren’t an abundant species back then,” he said.

By the 1970s or early ’80s, the frog was likely on the decline.

“In 1991, we started looking,” said Peterson. “There was an observation of one. ... up by the Flagg Ranch area in the early 1990s. I’ve gone back [to the park] a couple of times and looked for them.”

The frogs have also declined or disappeared from the surrounding region. Stable northern leopard frog populations used to exist places such as Victor, Idaho. Populations still exist near Ashton, Idaho.

“Leopard frogs were the most abundant amphibian in southern Idaho in the ’70s,” said Peterson. “My ballpark estimate is that they’ve disappeared from 80 percent of the places they used to be. In northern Idaho, I think they’re just gone up there.”

The reason for the frog’s decline is likely complicated, said Peterson. It  comes as researchers document the disappearance of other amphibians across the planet. 

“To have such a widespread loss like that would suggest to me that disease is involved,” said Peterson, who explained that pathogens such as the rana virus and the chytrid fungus have taken a toll on frogs in the United States and other countries.

Still, disease probably isn’t the whole story.

“Drought can make a disease worse,” Peterson continued. “It can stress them. Seldom does a species decline for just one reason.”

In addition to drought, development and pesticides have also proven detrimental to frog populations. The construction of the Jackson Lake Lodge, the rerouting of a road near Yellowstone Lake and the damming and channelling of the Snake River are all examples of how incremental development has impacted amphibian habitat in Grand Teton and Yellowstone parks. Even small changes in water temperature or water chemistry can make an amphibian more susceptible to disease.

Debra Patla, a research associate at Idaho State University participating in an amphibian inventory monitoring program with the National Park Service, said she and other researchers are holding out hope that a population of leopard frogs still exists in the park.

“They might be out there, we just haven’t found them yet,” she said. “When they’re there, you really see them. They’re a conspicuous frog because they jump. They go leaping into the water. They’re very vocal too. There have been reports, but they have not been documented since 1995.”

Peterson agreed. He recently received a report of a leopard frog near Phelps Lake, but unfortunately the species is often confused with spotted frogs.

“They’ll seem to disappear from an area and then they’ll come back,” he said. “I think ... in drought conditions a lot of amphibians will go locally extinct.”

“I don’t think the current drought is the answer,” Peterson continued. “Amphibians have had to deal with wet and dry conditions. You always expect population fluctuations in amphibians. Are we looking at a population fluctuation or actual long-term declines? I think for leopard frogs, it is pretty clear that it is a long-term trend.”

If leopard frogs do get Endangered Species Act protection, reintroducing them to the park isn’t out of the question, Patla said.

“There are reintroductions for other amphibian species,” she said.

“I still have hopes that they’re out there somewhere,” Patla continued. “But, as the years go by, I get less and less optimistic.”

Erin Robertson, biologist for Center for Native Ecosystems, one of the groups that petitioned the U.S. Fish and Wildlife Service to consider listing the leopard frog, said the species is one indicator of a larger problem.

“There’s a worldwide decline in amphibians, and this is an example of a decline that is happening locally right now,” she said.

The northern leopard frog is 2 to almost 5 inches long, green, brown or yellow, with large oval dark spots surrounded by a lighter halo and is found along streams and rivers, wetlands, permanent or temporary pools, beaver ponds and also permanent bodies of water depending on its life stage, according to the Fish and Wildlife Service.

Along with spotted frogs, boreal chorus frogs, boreal toads and tiger salamanders, northern leopard frogs are one of five native species of amphibian in the park. Bullfrogs also live in the park but were introduced by humans, according to the Park Service. 

The northern leopard frog is endemic to 19 states including Wyoming, Idaho, Montana, Colorado and South Dakota, and while some populations seem to be thriving, others have faded away over the years.