One of the Endangered Species Act’s strongest provisions, designation of “critical habitat” is required for all domestic species listed under the Act. Critical habitat includes specific areas within a species’ current range that have “physical or biological features essential to the conservation of the species,” as well as areas outside the species’ current range upon a determination “that such areas are essential for the conservation of the species.” In other words, the original definition of critical habitat said it must include all areas deemed important to a species’ survival or recovery, whether the species currently resides in those areas, historically resided in those areas, uses those areas for movement, or needs them for any other reason. Despite the obvious importance of critical habitat, both the U.S. Fish and Wildlife Service and the National Marine Fisheries Service — the agencies required by law to designate critical habitat — have been hesitant to protect it. We a...