Emperor penguin populations could plummet 19% by the end of the century, thanks—not surprisingly—to climate change, according to a new study. Emperor penguins breed and raise their chicks on Antarctica’s fringe of sea ice, and a constant amount of the frozen ocean water is vital to their survival. Too little sea ice, which harbors the penguin’s diet of squid, fish, and shrimplike critters called krill, means the penguins could go hungry. Too much ice and the birds have to travel farther to reach the ocean—a tough round trip for nonbreeding adults, but particularly for parents feeding their chicks. Climate change can have both direct and indirect impacts on sea ice extent in a given location, by not only warming temperatures and melting the ice, but also by altering wind patterns and wave heights that can push the ice around. Now, researchers have used climate projections of sea ice cover at the location of 45 known colonies to assess the impact of sea ice gain or loss on future penguin populations. Using demographic data from the well-studied colony at Terre Adélie in East Antarctica (the subject of the documentary March of the Penguins), the team determined that at least 75% of the emperor penguin colonies are vulnerable to changes in sea ice, they found, with 20% of the colonies heading for extinction by 2100, the team reports online today in Nature Climate Change.