Traditionally, the bird order Apodiformes contained three living families: the swifts (Apodidae), the tree swifts (Hemiprocnidae), and the  hummingbirds (Trochilidae). In the Sibley-Ahlquist taxonomy, this order is raised to a superorder Apodimorphae in which hummingbirds are separated as a new order, Trochiliformes. With nearly 450 species identified to date, they are the most diverse order of birds after the passerines.