As their name implies (Apodiform = "unfooted"), swifts and hummingbirds are exceptional flyers. They have light bodies, long wings (thanks to a long hand bone), and tiny feet that work for perching, but not walking. Their tapering wings beat rapidly for fast, agile flight. Swifts stay aloft for extraordinary periods of time, generally spending the whole day flying, perching only at night. Hummingbirds look like bees because of their unique ability (amongst birds) to hover, their wings making a buzzing sound as they beat up to 80 times per second. They fly forward and backward, rotating the outer (hand) part of their wings to maneuver. Hummingbirds hover while feeding on plant nectar that fuels their high-energy flight. Both swifts and hummingbirds catch insects on the wing by opening their mouths wide while flying. Some swifts and hummingbirds make migrations of hundreds of miles to warmer areas during the winter.

All modern birds have bills and no teeth. The shape of a bird's bill says a lot about what it eats, for example whether it specializes in seeds (stout , cracking bill), fish (pointy, spearing bill), or plants (wide, serrated bill). Birds swallow their food without chewing, so it travels to the stomach whole or in large pieces. Bird digestive tracts have some special features for digesting chunky food. A pouch in their throat (the crop), is used to store food to be digested later, or regurgitated to feed the young. An extra, muscular stomach (the gizzard) grinds food up. Birds are endotherms, using heat they make internally to keep warm. While a few species allow their body temperature to drop at night (torpor), a nearly constant body temperature is maintained by most birds most of the time. Continuously making heat requires fuel to burn, in the form of food. So, birds spend a lot of time eating.