- Main article: Ornithology
Apodiformes is an order containing three extant families - swifts, treeswifts, and hummingbirds. These birds have small legs and long wings, ideal for the hovering characteristic of hummingbirds.
Apodidae is derived from a Greek word meaning footless, referring to the small weak legs found on birds of this family. Swifts are the fastest birds, and are able to rotate their wings at the base, unlike most birds. They live on all continents except Antarctica. They are characterized by a short forked tail and long wings that resemble a boomerang. Most species of swifts glue their nests to a vertical surface using saliva; the saliva is the basis for bird's nest soup. Swifts' diet consists of insects.
Hummingbirds gain their name from the humming sound created by their wings beating at high speeds. They are one of the smallest birds, and have the highest metabolism of all birds. All hummingbirds depend on flower nectar for food, but they have evolved to have different beak shapes to suit different flowers. Most hummingbirds build a small cup-shaped nest on a shrub or tree branch, and often use spider silk to bind the nest together, allowing it to expand as the young grow.