Resemblances between swifts and swallows are due to convergent evolution, reflecting similar life styles based on catching insects in flight.

[1] The family name, Apodidae, is derived from the Greek ἄπους (ápous), meaning "footless", a reference to the small, weak legs of these most aerial of birds.

Analysis of behavior and vocalizations is complicated by common parallel evolution, while analyses of different morphological traits and of various DNA sequences have yielded equivocal and partly contradictory results.

[6] Cypseloidinae Apodinae Swifts are among the fastest of birds in level flight, and larger species like the white-throated needletail have been reported travelling at up to 169 km/h (105 mph).

Changing the angle between the bones of the wingtips and forelimbs allows swifts to alter the shape and area of their wings to increase their efficiency and maneuverability at various speeds.

Young birds reach a maximum weight heavier than their parents; they can cope with not being fed for long periods of time, and delay their feather growth when undernourished.

[16][17] All swifts eat insects, such as dragonflies, flies, ants, aphids, wasps and bees as well as aerial spiders.

[21] Over-harvesting of this expensive delicacy has led to a decline in the numbers of these swiftlets,[22][23] especially as the nests are also thought to have health benefits and aphrodisiac properties.

The nests are composed of interwoven strands of salivary cement and contain high levels of calcium, iron, potassium, and magnesium.