Classification The phylogenomic relationship between Apodiformes and Caprimulgiformes has been discussed under the latter order. Note that the two orders cannot coexist as defined if paraphyly of Caprimulgiformes is to be avoided.

The swifts (Apodidae) and the hummindbirds (Trochilidae) are very different from one another in general appearance and way of life. The most obvious common characteristic of the two groups is a superb mastery of the air; both swifts and hummingbirds  share some peculiarities of wing structure. In addition, swifts and hummingbirds are among the few groups of birds that have been shown to be capable of energy conservation through a reduction of their body temperature and entry into a torpid (sluggish) condition. Some ornithologists believe that these resemblances are convergent (the result of the same type of natural selection acting on unrelated organisms), but genetic analyses have convincingly shown that the two groups share a common ancestor.

Swifts are in most parts of the world often confused with swallows, which are unrelated but generally similar to swifts in size, proportions, and aerial habits. Swifts drink by swooping down at the surface of a body of water, and nesting material may be picked in midair or snatched in full flight, as are grass stems. Swift courtship displays are wholly aerial, and copulation is known to take place in full flight.

In foraging,  most hummingbird species depend upon their unique ability to hover, motionless except for beating wings and darting tongue. They can even fly backward or upside down for short distances. The basic food is flower nectar.

Two sister families, not shown here, are also included in the Apodiforme order, namely the owlet-nightjars (Aegothelidae) and the treeswifts (Hemiprocnidae). They share a sister relationship with the swifts and hummingbirds.

Hackett SJ et al (2008): Phylogenomic Study of Birds

apodiform. (2011). Encyclopædia Britannica Ultimate Reference Suite.  Chicago: Encyclopædia Britannica

http://en.wikipedia.org/wiki/Apodiformes