An order of birds consisting of two dissimilar groups, the swifts (Apodi) and the hummingbirds (Trochili). These birds have been placed together because of several anatomical specializations of the wings and feathers, although an alternative classification based on morphological and molecular characters places the swifts and hummingbirds in two separate orders. Swifts and hummingbirds have strong wings and are excellent fliers but have small, weak feet and cannot walk. Some of these features may be convergences because of the rapid but different flight of these birds. The two groups share a unique crossover structure of a superficial neck muscle which cannot be related to their ways of life. The relationship of the swifts and hummingbirds to other birds is obscure.