Species of frogs that vanished may be on the rebound

In 2013, two biologists named Jamie Voyles and Corinne Richards-Zawacki spent weeks slogging up and down mountainsides in Panama. “We were bug-bitten and beat up,” recalled Voyles, now an assistant professor at the University of Nevada, Reno.

Near the end of their trek, they came to a stop. In front of them sat the object of their quest: a single gold-and-black frog.

“I can’t tell you what that moment was like,” Voyles said.

She had feared that variable harlequin frogs had disappeared entirely from Panama. As recently as the early 2000s, they had been easy to find in the country’s high-altitude forests.

“They used to be so abundant that you could barely walk without stepping on them,” Voyles said.

But in recent years, Voyles and her colleagues started to encounter sick frogs, and then dead ones. And then they couldn’t find any variable harlequin frogs at all.

Many other species at Voyles’ research sites in Panama suffered the same grim fate. As had frogs around the world. Voyles and other frog researchers found that many of the dead frogs were covered with the same aggressive skin fungus, known as Batrachochytrium dendrobatidis or Bd.

As Bd spread from forest to forest, and continent to continent, researchers feared that amphibians might suffer mass extinctions. Today, many species of frogs and toads are still dwindling, and some have disappeared altogether.

But scientists like Voyles have also found a little cause for hope: a handful of species appear to be coming back. After discovering variable harlequin frogs again, she and her colleagues have returned to their Panama research sites and found a few other species that had previously vanished.

“They’re not in large numbers — their abundances are low,” Voyles said. “But we think that as more time goes by, we’ll find more species that we thought were lost.”

Now scientists are trying to figure out what accounts for these rebounds. On Thursday, Voyles and her colleagues published evidence suggesting that the frogs have gained potent defenses in their skin against the fungus.

But other experts are divided about whether the researchers found a cause of the rebound. It’s possible that there are other causes at work. Even climate change — which is posing its own threats to many frog species — may be temporarily helping some frogs withstand the fungus.