MOSCA — A frog that hasn't been seen at Great Sand Dunes National Park and Preserve in more than 40 years has returned.
Ranger Patrick Myers said he spotted a northern leopard frog July 31 during a nature walk with visitors in the South Twin Lake area managed by The Nature Conservancy.
In two more walks since then, he's seen more of the green frogs with black spots.
Myers said he and visitors have seen about 10 of the frogs this summer. Each was about 2 inches long and less than a year old. Adults grow to 3 to 4 inches.
"It's a good sign for the ecological health of the park," Myers said. "Amphibians are thought of as indicator species, like a canary in the mine."
With porous skins that make them susceptible to toxins and pollutants, amphibians are often among the first animals in an ecosystem to disappear when habitat changes.
Researchers have speculated that disease, altered habitat or other frogs could have forced the northern leopard frogs from the park.
It was unclear why they returned, but there is now a healthy population about four miles south of the park, Myers said.
"You hear so much about environmental degradation in our nation and things disappearing," Myers said. "It's kind of neat to have a positive thing."
The South Twin Lake area also is frequented by three kinds of toads, other frogs and tiger salamanders, Myers said.