Environmental groups have sued (PDF) the Fish and Wildlife Service to force the listing of the Sonoran desert tortoise in Arizona as a distinct population segment under the Endangered Species Act.  The lawsuit is the latest legal development that threatens to slow or block the national effort to promote the development of solar energy on federal lands in the Arizona desert.  The listing of a related population of desert tortoise across the border in California has triggered significant limitations on solar projects in the Mojave Desert. 

On August 28, 2009, the Fish and Wildlife Service announced its finding (PDF) that the listing of the Sonoran desert tortoise may be warranted.  According to the lawsuit, the Service received a petition to list the tortoise in October 2008.  Under the ESA, the Service then had until October 2009 to make its 12-month finding that listing the tortoise as endangered or threatened is "warranted," "not warranted" or "warranted but precluded" by other listing actions of higher priority.  If listed, projects that harm the tortoise will be required to obtain incidental take authorization from the Service.  Listing will also trigger the requirement to designate critical habitat which will impose additional restrictions on solar energy development.