Small, compact night bird with short wings and tail. Intricately patterned with shades of gray; flight feathers are barred with rufous. Males have white corners on tail, females have browner tail corners. Named for its song: a whistled "poor-WILL," sometimes with a faint third note. Strictly nocturnal; more often heard than seen. Prefers rocky desert slopes with some dry vegetation; sometimes perches prominently when singing but also sings from the ground.