Monarch butterfly populations have decreased by 80 percent since the 1990s. Now scientists may be able to figure out why. In the fall, they were able to track the migration of individual monarch butterflies for the first time as they flew from as far north as Ontario, Canada, to their winter colonies in Mexico. The breakthrough came as the result of a new ultralight solar-powered radio tag that transmits a signal revealing its location. Researchers tagged more than 400 monarchs and followed their journeys on an app called Project Monarch Science. It’s a step up from previous low-tech efforts to track monarchs, such as tagging them with stickers that provided only basic information, such as where and when they were tagged. Now scientists can actually see the migration path. So far, they’ve found that many monarchs are blown off course but use their strong wing muscles and remarkable navigational abilities to get back on track. The new tags could also provide insights into the poorly understood life cycles of hundreds of species of insects at a time when many are in steep decline. “There’s nothing that’s not amazing about this,” says Cheryl Schultz, a butterfly scientist at Washington State University. “Now we will have answers that could help us turn the tide for these bugs.”