OGDEN, Utah (AP) — Biologists in Utah are working to save native boreal toads from extinction in the face of the destruction of its habitat by humans and competition from invasive species like bullfrogs.

Boreal toads are tough to track. They blend in well with their environment, they're mostly active at night and they're not vocal. The only sound they make is a little squeak males use to keep other males away, the Standard-Examiner reports (http://bit.ly/2w9ECNj ).

That makes it hard for biologists to pin down how many toads live in Utah — but their yearly surveys indicate populations have taken a massive hit.

"It's clear they are declining," said Kayleigh Mullen, citizen science biologist with Utah's Hogle Zoo. "That decline is widespread. It's happening here. Something has to be done."

Part of the problem causing amphibian declines, including boreal toads, is a fungus-caused disease — chytridiomycosis, or "chytrid." It thickens amphibians' skin so they can't absorb water or nutrients, and they dry out and die.

The toads' biggest challenge, however, comes from people. "The number one most common threat is simple habitat destruction," said Jenny Loda, reptile and amphibian staff attorney at the Center for Biological Diversity.

In the southern Rocky Mountain region, which includes Utah, the center estimates boreal toads have been reduced to one percent of their historic breeding range.

The animals require a unique blend of habitat to thrive — ponds with sloping bottoms so they can lay eggs in the shallows, land vegetation to hide from predators, and burrows to hibernate.

Grazing and recreation are altering that habitat in big ways.

In south-central Utah, state biologists found a handful of boreal toads for the first time in years. They had deposited eggs in a water-filled tire rut.

Elsewhere in the state, invasive, water-sucking plant species have moved in. Humans have brought several other species to the West that are wreaking havoc for the boreal toad as well, including bullfrogs.

Bullfrogs are also more resistant to chytrid, but they carry the disease and spread it to native populations.

Then there are water diversions and human-caused climate change that have drastically altered the wet environments where toads thrive.

Still, toads in Utah's northern regions are doing better than populations elsewhere in the state.

"We're starting to see some stability with our populations," said Cody Edwards, native aquatics biologist for the Utah Division of Wildlife Resources Northern Region. "They're not growing, but they've declined and now they're somewhat holding at where their lower numbers are at."

One population in the Grouse Creek Range seems to be adapting to its environmental demands. Those boreal toads are breeding at human-made ponds for livestock, around 2,000 feet below their normal elevation range.

Some biologists theorize the Grouse Creek toads might be fighting off chytrid, too, because they're in a hotter and drier climate than most boreal toad populations.

While much of the boreal toad's life cycle and habits remain a mystery, scientists are getting a better sense of their movements through tagging and monitoring efforts like those DWR has done. And those efforts were largely fueled by efforts to keep the toads off the endangered species list.

Environmental groups like the Center for Biological Diversity have long-fought for an endangered species listing since the 1990s. After reaching a settlement, the U.S. Fish and Wildlife Service will likely issue a listing decision on the boreal toad by the end of September.