Twenty-five percent of mammals are classified as threatened, and the overall risk of extinction increased for the group between 1996 and 2008, the period used to measure mammal vulnerability. The researchers found that the extinction risk for mammals as a group increased by 0.8 percent in that period. That comes out to 156 mammals species moving one or more categories closer to extinction. No mammals species went completely extinct in that time period.
Conservation efforts partially counteracted the increase in vulnerability; the researchers estimated that the risk for mammals would have increased by 0.94 percent in their absence. The difference was roughly equivalent to 29 species being taken at least one step further from extinction.