The Mojave Desert tortoise is a relatively large reptile, with adults measuring up to 15 inches in shell length (see fig. 1). Desert tortoises live in creosote bush and Joshua tree habitats in valleys, plains, and washes at elevations generally ranging up to 4,000 feet above sea level. In these habitats, desert tortoises construct and live in burrows and spend a majority of their life below ground. Desert tortoises may live for 50 years or more in the wild, and females do not breed until they are at least 15 years old. They usually lay one or more clutches of about 6 to 8 eggs between mid-April and the first week of July. Although desert tortoises can withstand prolonged periods of drought, females may not lay eggs if forage is unavailable. Survival of juveniles is thought to be low; some researchers estimate that only 2 to 3 per 100 hatched may live to become adults. The Mojave Desert tortoise’s range lies north and west of the Colorado River in California, southern Nevada, southwestern Utah, and northwestern Arizona (see fig. 2). Apparent declines in tortoise populations have been attributed to many factors including habitat loss or degradation, drought, and predation on juvenile tortoises by ravens, coyotes, domestic dogs, and other animals (see fig. 3). According to the Service, habitat loss has occurred as a result of increasing amounts of urban development, military operations, and recreational uses such as off-road vehicle use, in the tortoise’s range. Habitat degradation has been attributed to domestic livestock grazing, particularly in livestock watering and loading areas. Other factors that may have caused population declines include mortality through vandalism or accidental road kill and removal of tortoises from their habitat for pets, food, or commercial purposes. Respiratory and shell diseases have also been observed in desert tortoise populations. Before a species, such as the desert tortoise, can receive protection under the Endangered Species Act, the Secretary of the Interior, through the Fish and Wildlife Service, is required to use the best available scientific and commercial data (e.g., biological or trade data obtained from scientific or commercial publications, administrative reports, maps or other graphic materials, or experts on the subject) to decide whether the species is at risk of extinction. The Endangered Species Act specifies the following five factors for identifying at-risk species, any one of which is sufficient to determine that a species qualifies for the act’s protections: present or threatened destruction, modification, or curtailment of a species habitat or range; overuse for commercial, recreational, scientific, or educational purposes; disease or predation; inadequacy of existing regulatory mechanisms; or other natural or manmade factors affecting a species’ continued existence. Once the Service determines that a species should receive the act’s protection, it can list the species as threatened or endangered. As of July 2002, 517 animal species and 744 plant species were listed as threatened or endangered in the United States. The act prohibits the “taking” of any listed species of animal and defines “take” as to harass, harm, pursue, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct. However, under the act the Service may issue permits that allow the taking of a listed species if the taking is incidental to, rather than the purpose of, an otherwise legal activity. In most cases, the Service must develop a recovery plan for listed species that specifies actions needed to recover the species so that it can be removed from the list of protected species under the act, or “delisted.” Federal agencies must comply with prohibitions against taking a threatened or endangered species and must consult with the Service to determine the effect, if any, that their activities may have on listed species. In particular, federal agencies must ensure that their activities do not jeopardize the continued existence of any endangered or threatened species, or result in destruction or adverse modification of critical habitat.If any proposed activities will jeopardize a species or adversely modify its critical habitat, the Service will identify reasonable and prudent alternative activities. In addition, federal agencies have a broader directive under the act to use their authorities to carry out programs to conserve threatened and endangered species. Scientists we consulted agreed that the listing of the desert tortoise in 1990, the critical habitat designation, and the recommendations in the recovery plan were reasonable, based on the limited data available on the desert tortoise when the relevant decisions were made. These decisions were made on the basis of a variety of information, including published and unpublished research and government studies. The scientists we consulted recognized that, as is often the case when making such decisions, little published data on the species were available. However, they agreed that the Service’s decisions were appropriate and consistent with their understanding of the agency’s responsibilities under the act. The Endangered Species Act requires that listing decisions be based solely on the best scientific and commercial data available without taking into account economic factors. Although the Service is required to seek out the best data available at the time, it is not required to generate additional data. The listing decision for the desert tortoise was based on a variety of information, including published research, meeting and symposium proceedings, and government reports. Generally, published, peer-reviewed research is considered the most reliable information source because the research methods and conclusions have been reviewed by other scientists before publication. However, other sources such as unpublished research, meeting proceedings, and government reports can provide important information for making listing and other decisions. Moreover, several scientists said that listing decisions are often necessarily based on limited data, because funding for research on a species is typically scarce until after that species is listed. The listing decision describes how each of the five listing criteria that make a species eligible for protection under the act applies to the desert tortoise, with habitat loss and disease cited as threatening the tortoise’s continued existence. The scientists we consulted agreed that, despite the limited amount of quantitative data on the desert tortoise that was available at the time of its listing, the decision to list it as threatened was reasonable. In particular, they cited increases in threats such as diseases and habitat loss as important factors making listing necessary. In addition, researches noted declines in numbers. For example, in the western Mojave Desert in California, researchers found that some populations decreased by as much as 90 percent between the 1970s and the mid-1990s; in Nevada, study plots also generally showed declines ranging from 10 to 39 percent since the late 1970s. The scientists we consulted also noted that desert tortoise populations appear to continue to decline. Some said that the listing of the desert tortoise was an unusual step by the Service because, at the time of the listing, there were still desert tortoises occurring across a large range; yet they recognized that listing it as threatened was consistent with their understanding of the act’s intent to protect species whose numbers are declining and are at risk of becoming endangered. When designating critical habitat, the Service must also use the best scientific and commercial information available. Unlike for listings, however, the Service must also consider the economic impact of the critical habitat designation. The primary source of information for the designation was a draft of the recovery plan for the tortoise that recommended protection for 14 separate areas of habitat. The Service adjusted the boundaries for these 14 areas to generally follow legal property boundaries and elevation contours in order to remove as much unsuitable habitat as possible and to reflect additional biological information. Some areas that were already protected, such as Joshua Tree National Monument and the Desert National Wildlife Range, were intended to be excluded from critical habitat because the habitat within them was already receiving protection as desert tortoise habitat. After making these adjustments, the Service identified 12 areas in its final critical habitat designation—seven in California, one in Nevada, one in Utah, and three that span more than one state—that total about 6.4 million acres (see table 1). The scientists we consulted said the size and number of the areas designated as critical habitat were reasonable given the available data, but found that the rationales for drawing the specific boundaries were not well explained in the decision documents. The size of the areas was determined based on estimates of how dense a desert tortoise population should be to ensure the population’s continued existence—estimates that the scientists noted were based on limited quantitative research. Several of the scientists we consulted observed that the critical habitat areas appear to have been designated where desert tortoise populations were found at the time. One scientist suggested that the designation of the areas of critical habitat may have been conservative, and that if the designation was done today, the protected areas might be even larger. In contrast with the requirements for listing and critical habitat, the Endangered Species Act does not specify the type of information that should be used to develop recovery plans. Instead, the act requires that recovery plans contain three specific elements: (1) a description of site- specific management actions necessary for the conservation and survival of the species; (2) objective, measurable criteria that, when met, would result in the removal of the species from the threatened or endangered species list, or delisting; and (3) estimates of the time and cost required to carry out the plan. However, Service policy dictates that recovery plans should seek the best information to achieve recovery of a species. While not in effect at the time the tortoise recovery team was founded, Service policy is that teams developing recovery plans should have diverse areas of expertise and may include personnel from many different organizations, including officials from other federal agencies and states, and other recognized experts. According to the Service, recovery plans impose no obligations on any agency, entity, or persons to implement the various tasks contained within them. The recovery plan for the desert tortoise addresses each of the three required elements.