The Black-capped Gnatcatcher is almost endemic to northwest Mexico, but just creeps into extreme southeast Arizona in the United States. It prefers dry woodlands and thorn scrub habitats, and is usually fairly common in such areas. The sexes differ in that females lack the very extensive and glossy black cap of the males, which reaches well below the eyes and contrasts with the pale eye-ring. Females also have a pale eye-ring. Although generally considered to be resident, it is possible that at least some individuals of the species’ northernmost populations move south in the post-breeding season.