Critical habitat designation under the US Endangered Species Act: How are biological criteria used?

Critical habitat designation under the US Endangered Species Act (ESA) is not working as Congress intended. Issues include the use of science during designation, the costly and litigious delays in designation that have led to repeated lawsuits, and the potential overlap with other ESA protections. In this paper, we address a neglected aspect of critical habitat designation: how the biologically-based designation criteria of the US Fish and Wildlife Service are used during the designation process. We primarily examine whether taxon (within terrestrial animals) or legal status (whether critical habitat was designated after a court challenge) affect the use of the criteria. Court-ordered cases used more criteria than non-court-ordered cases. There were also differences in use of criteria with respect to taxon and region, and a weak relationship with the year of designation. Criteria that focused on discrete elements, such as nest sites or locations where required food species occurred, were used more often than criteria that addressed broader ecological needs such as space for normal behaviour or representation of historic range conditions. Revising the critical habitat designation criteria and enforcing their consistent use during designation would be helpful for conservation of imperiled species in the United States.