By the numbers: how is recovery defined by the U.S. Endangered Species Act?

Nearly 40 years after passage of the US Endangered Species Act, the prospects for listed species remain dim because they are too severely imperiled by the time they receive the act's protection. Even if threats are abated, the low abundances required for recovery often preclude a high probability of persistence. The lack of sufficient data for setting recovery objectives also remains a barrier. Delisting is considered possible for only 74% of the 1173 species with recovery plans—92% of threatened and 69% of endangered species. The median number of populations required for delisting (8) was at or below the historical numbers for 64% and at or below the numbers at listing for 37% of the species. The median number of individuals required for recovery (2400) exceeded the abundances at listing for 93% of the species, but most were below the levels considered necessary for long-term persistence, especially in changing environments.