Mammals in global decline.

• Author: Runyan, Curtis

Nearly one-fourth of the world's known mammal species are threatened with extinction, according to a recent study compiled by the IUCN-World Conservation Union, which suggests that earlier estimates of the number of endangered species may have been too low. The latest update in a series known as the Red List, the report is the most comprehensive evaluation of globally threatened animals ever compiled, and the first to assess all known mammal species.

Until now, birds were the only group fully assessed. With 11 percent of all bird species facing the threat of extinction and 70 percent experiencing population declines, scientists had relied largely on the status of birds as an indicator of the level of threat to all terrestrial life-forms (see "Flying Into Trouble: The Global Decline of Birds, and What it Means," January/February 1994).

The number of mammals on the Red List - a shocking 1,096 of the 4,630 known species - has spurred calls for an intensified international focus on biodiversity loss. The report also found that nearly one-third of all 275 primate species are at risk, almost three times the number of previous estimates (see note below).

The new survey was compiled using a revised set of criteria, which the authors described as more objective than those used in previous estimates, to determine the threat of extinction. Based on 35 years of data from more than 500 scientists worldwide, the report found that 5,205 vertebrates of all kinds are endangered, including 25 percent of amphibians, 20 percent of reptiles, and 34 percent of fish. More than 100 species of marine fishes were added this year, suggesting that fish, too, could be at a higher risk than previously thought.

The Red List recognizes three distinct categories of risk: of the 1,096 species of mammals considered threatened, 169 are listed as "critically...