Since at least the 1970s, frog populations have been in decline. A new study in Proceedings of the National Academy of Sciences reports that at least 3.1 percent of frog species have gone extinct, and another 6.9 percent may disappear within the next century. John Alroy, a biologist at Macquarie University in Australia and the study’s author, computed extinction probabilities for species of frogs around the world by building a statistical model based on sighting frequency and last date of sighting. Frogs are at risk for a number of reasons, including epidemics caused by pathogens like the fungus B. dendrobatidis; deforestation; invasive species; and climate change.