The greater sage grouse (Centrocercus urophasianus) is the largest North American grouse and gives the illusion of being the proudest. On mating grounds, males flaunt erminelike neck wraps while inflating bright yellow air sacs on their breasts. As many as 16 million grouse once ranged the western steppe, according to some estimates; today, the population is believed to have dropped to fewer than 500,000. The decline “all boils down to habitat loss,” says Connelly, considered a leading expert on the bird. Sage grouse are entirely dependent on sagebrush, a low, woody shrub, to survive. But sagebrush ecosystems are among the continent's most imperiled, eroded by drought, fire, and invasive species—and by development.