Measuring progress in US endangered species conservation.

Since passage of the Endangered Species Act in 1973, over 1300 endangered and threatened species have been protected in the USA and its territories. Most species continue to face a significant risk of extinction, but the status of many species is improving. Here we present analyses of federal agency reports to the United States Congress (1988-2002) that describe differences in species status and show which variables are correlated with improving or declining status.