Australia's iconic koala is at risk as its habitat comes under increasing threat from human development. But the koalas also create problems of their own: Many will eat only certain species of eucalyptus, limiting their food intake. Now, a new study suggests why the koalas are such picky eaters—it's their gut bacteria, Nature reports. After collecting feces from 200 koalas at 20 sites, scientists found that koalas with different eucalyptus preferences harbored different gut bacteria. Researchers then transferred fecal bacteria from one group to the other. Within about 2 weeks, the koalas could eat the strain of eucalyptus they were unable to digest before, researchers reported at the annual meeting of the American Society for Microbiology. The finding could help save the koala—and other species with limited food supplies.