When Jack Connelly first began studying the greater sage grouse in Idaho in the late 1970s, “it was not unusual to see 500 in a single flock,” says the biologist, who is retired from the Idaho Department of Fish and Game. “Today, it would be unusual to see 200.” That dramatic decline has made the sage grouse—a large, pointy-tailed bird with showy mating habits—the subject of one of the biggest endangered species battles ever in the United States. President Barack Obama’s administration is under court order to decide by 30 September how to protect the bird: declare it an endangered species—the nuclear option in conservation—or opt for the less onerous conservation strategies that officials are testing on its fellow rangeland bird, the lesser prairie chicken. An endangered listing could have widespread economic and environmental consequences. The sage grouse’s remaining population is spread over 67 million hectares in 11 western states, pitting it against farming, ranching, mining, and energy interests. Some members of Congress are trying to block any listing, because of the potential cost to industry and private landowners. They have even vowed to stop ongoing government efforts to protect grouse on federal lands, which hold about 65% of its key remaining habitat. “I don’t think it’s an overstatement to say that this issue is the mother of all [endangered species] decisions,” says forestry scientist Eric Washburn, of the law and lobbying firm Bracewell & Giuliani in Washington, D.C.To read the full story, see the 19 June issue of Science.