In 2013, two biologists named Jamie Voyles and Corinne L. Richards-Zawacki spent weeks slogging up and down mountainsides in Panama. …In front of them sat the object of their quest: a single gold-and-black frog. …“They used to be so abundant …But in recent years… they couldn’t find any. …As had frogs around the world. Dr. 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. …Now scientists are trying to figure out what accounts for these rebounds. Dr. Voyles published evidence suggesting that the frogs have gained potent defenses in their skin against the fungus. …Even climate change may be temporarily helping some frogs withstand the fungus.