A new survey of the world's 5,487 mammal species reveals that one in four is in danger of dying out—including some species of bats, the most numerous of mammals. The International Union for Conservation of Nature (IUCN) concludes that at least 1,139 mammals around the globe are threatened with extinction and that the populations of 52 percent of all mammal species are declining. South and Southeast Asia are home to the most threatened mammals. Deforestation and hunting are the prime causes of the rapid declines in land mammals, such as elephants in Asia; most endangered marine mammals, such as the vaquita porpoise in Mexico's Gulf of California, have succumbed to fishing nets, ship strikes or pollution.

Concerted efforts have brought some mammals, such as the black-footed ferret, back from the brink, but long-term success depends on tackling the root problems, the IUCN warns in its report published in the October 10 Science.