PACIFIC GROVE, CALIFORNIA—Pikas are champs when it comes to keeping warm in cold weather. But this adaptation comes at a cost, one that may make it impossible for these small mountain-dwellers to cope with climate change. As their habitats heat up, pikas living at low elevations have one major shot at avoiding extinction: migrating to cooler, higher parts of the mountain. But even if they can make the shift, low-altitude pikas might not be able to cope with the low oxygen of higher altitudes, biologists reported here last week at a meeting of the American Society of Naturalists. Pikas, which include about 30 species all living at different altitudes, have likely evolved special adaptations for living where they do. To assess functional differences between high-, low-, and midaltitude dwellers, researchers compared 10 species from elevations ranging from sea level to 5000 meters. They looked at three genes in the cell’s powerhouses, the mitochondria. These genes code for proteins that help use oxygen to generate chemical energy for the body. The proteins from high-altitude pikas appear to be very efficient at this conversion, which helps explain how they thrive high up where the air is thin. Low-altitude pikas have a modified version that seems to generate lots of heat but less fuel for the cell. That’s great for keeping toasty, but it could make survival that much harder if they have to move to higher altitudes, where efficient oxygen use is critical. And if the pika falters, it could mean trouble for an entire ecosystem: On the Tibetan Plateau, they are the most common small mammal to stay active through winter, providing one of the few foods for snow leopards, weasels, even bears. Moreover, with up to 60 entrances to each one’s underground burrows, they turn parts of the landscape into a “sponge” that soaks up monsoon rains and slows runoff, helping to keep rivers full year-round.