The family Apodidae includes 9 species found in North America.
Typical Swifts range in size from 10-25 cm in length and vary in weight from 6.5 to ca. 200 gms. Plumage is hard without downy or silky feathers. The apodid swifts are the most aerial of birds, feeding, drinking, bathing and copulating in flight and several species (e.g., Apus apus) can spend the night on the wing. Plumage colors are mainly brown or gray with lighter patches; some species have iridescent areas. The short legs and strong claws are adapted for clinging to the vertical surfaces of trees, cliffs, etc.
Swifts forage entirely on the wing, feeding mainly on insects and spiders; occasionally they may take insects or spiders from the surface of the water, foliage or under the eaves of buildings. Most swifts glue nest material together with sticky saliva. Clutch sizes vary from 1-6 eggs. Incubation periods are 19-23 days. The nestling period is long and variable: 5-8 weeks in Apus apus depending on the weather which determines the supply of flying insects. Adults may forage far from the nest, returning to feed the nestlings with food items glued together with saliva and carried in the mouth.
Swifts - Patuxent Bird ID Center