We were about to quit for the afternoon on our tour through the Antasibe-Mantadia National Park in eastern Madagascar when the guide caught a flash of brown fur through the trees. He signaled to our traveling party silently, and we crept off the narrow path and through the thick tropical forest, hoping for a closer look. Russell Mittermeier, the president of Conservation International (CI) and a renowned primatologist, made the call. Tucked inside a hollow tree trunk were two greater bamboo lemurs, each the length of a forearm, staring back at us with orange eyes. We grabbed our cameras and began snapping. It was a rare sight too rare, with only around 150 individuals estimated to still be alive. "You're looking at the most endangered primate on the planet," said Mittermeier.
The critically endangered greater bamboo lemur, however, is far from alone. Thanks to deforestation, expanding human settlements, hunting and the slow burn of climate change, more mammals may be endangered today than ever before. According to a worldwide assessment overseen by the International Union for the Conservation of Nature (IUCN) and published Oct. 6 in Science, an estimated one out of four mammals is threatened with extinction. The populations of about half the 5,487 known species of mammals in the world, on land and in the water, are dwindling each year. "Our results paint a bleak picture of the global status of mammals worldwide," the study's authors wrote in Science. "Within our lifetime, hundreds of species could be lost as a result of our own actions," said Julie Marton-Lefevre, the IUCN's director-general, at the organization's annual congress in Barcelona. "We must now set clear targets for the future to reverse this trend to ensure that our enduring legacy is not to wipe out many of our closest relatives."
The IUCN assessment itself is an impressive and important work of science. Drawing on data from more than 1,700 experts in 130 countries, the five-year collaborative study tracked habitats, distributions and threats to every known species of mammal on the planet. That isn't as straightforward as you might think. New species are discovered constantly the total number of known mammalian species is up 19% since 1992. Though they're the largest type of animals, mammals range in size from the titanic blue whale to the tiny mouse lemurs of Madagascar, which can fit in the palm of your hand. What they have in common are clear threats from us. "Mammals are important because they play key roles in ecosystems and provide important benefits to humans," says Andrew Smith, a biologist at Arizona State University and one of the 103 authors of the Science study. "If you lose a mammal, you often are in danger of losing many other species."
The number one driver of extinction is habitat loss and degradation, which affects 40% of the world's mammals. That can be seen clearly in the deforestation afflicting much of the tropical world, including Madagascar, where 90% of the country's original forest cover has been lost. Vast stretches of the once verdant island, where I traveled with Mittermeier last month, are eroded wastelands, capable of supporting few animals or people. Though the rate of deforestation has been reduced sharply in recent years, thanks in part to a greener government, Madagascar's protected areas are still threatened by new mining projects and simple human population growth. Mammals like the greater bamboo lemur are highly sensitive to their environment; if we lose the small stretch of forests in the southeastern reaches of Madagascar that this animal calls home, there is nowhere else it can go. It will be lost. That story is being repeated throughout much of the world, where mammals like the Iberian Lynx, the Pere David's Deer in China and the Tasmanian Devil are all listed as threatened or worse on the IUCN's annual Red List of endangered species.
The Red List, however, isn't a death sentence careful conservation work can bring back species from the brink of extinction. The black-footed ferret in the western U.S. was believed to be extinct in the wild meaning it was only found in captivity until it was successfully reintroduced into the wild by the U.S. Fish and Wildlife Service between 1991 and 2008. Conservationists did the same work in Mongolia, where they successfully reintroduced wild horse to the steppes of Central Asia. And new techniques like selling the carbon sequestered in standing forests as a way to fight climate change offer the potential for game-changing new sources of revenue for conservation. Altogether, the IUCN assessment estimates that 5% of currently threatened mammals are showing signs of recovery. But that's just a drop in the bucket compared to the number of mammals whose populations are dwindling fast and nearly 900 species lacked the necessary data to be classified as safe or threatened. "The reality is that the number of threatened mammals could be as high as 36%," noted Jan Schipper, the director of the Global Mammal Assessment for CI. If we don't act soon, our children may live in a world where the only place they'll be able to see unique mammals like Madagascar's greater bamboo lemur will be in history books.