Males of most species are identified by their iridescent feathers. Females and immatures of both sexes are normally plain and nondescript with the immatures of both sexes resembling the adult females.
Hummingbirds are strictly a bird of the Western Hemisphere.
They are found as far north as Southeastern Alaska and the Maritimes of Canada and as far south as Southern Chile. The majority of the approximately 320 species are found in the tropics. Only 15 species have been known to breed in North America with another 6 being classified as vagrants. Until recently, for instance, it was thought that Ruby-throated hummingbirds were essentially the only species of hummingbird found east of the Mississippi River.