Distinguished from all other North American hummingbirds by its immaculate white underparts, iridescent bluish-violet crown, and red bill, the Violet-crowned Hummingbird reaches the northern end of its range in southeastern Arizona and southwestern New Mexico. There, it nests almost exclusively in the Arizona sycamore tree (Platanus wrightii), which, in the United States, is limited to the riparian zones of the arid Southwest. In Mexico, this hummingbird's range extends down the Pacific slope from Sonora through Jalisco to northwestern Oaxaca and in the interior Madrean Highlands from western Chihuahua south through Durango to Oaxaca. Within its Mexican range, it inhabits arid to semiarid scrub, thorn forests, riparian and oak woodlands, and parks and gardens. Fairly common in Mexico, it is uncommon and local in the United States.
The biology of this hummingbird remains poorly known; the only detailed natural history and behavioral studies have been conducted in Guadalupe Canyon in southwestern New Mexico and southeastern Arizona, where Baltosser ( Baltosser 1986a , Baltosser 1989b , Baltosser 1996 ) studied nesting behavior and habitat selection of this and other hummingbird species. His results provide groundwork for understanding the breeding biology of this species, although much remains unstudied.
The Violet-crowned Hummingbird is essentially resident throughout most of its range but may wander locally, visiting several habitats during the year following seasonal bloom of trees and shrubs ( Des Granges and Grant 1980 ). In the United States and northern Mexico, it is considered migratory but increasing numbers of overwintering records in Arizona seem correlated with increasing numbers of confirmed breeding areas. Perhaps this species is best viewed as a wanderer that is expanding its range northward.