Hummingbirds have traditionally been a part of the bird order "Apodiformes". This order includes the Hummingbirds, the swifts and the tree swifts. The Sibley-Ahlquist taxonomy of birds, based on DNA studies done in the 1970s and 1980s, have changed the classification of hummingbirds. Instead of being in the same order as the swifts, the hummingbirds were made into an order that only included themselves, "Trochiliformes". Their previous order, "Apodiformes" was changed to the superorder "Apodimorphae". This superorder contains the three families of birds which were in it when it was an order.