They are medium-sized nocturnal birds with long wings, short legs and very short bills that usually nest on the ground and catch flying insects. The Least Nighthawk, at 16 cm (6.3 inches) and 23 grams, is the smallest of all Caprimulgiformes. Nightjars are sometimes referred to as goatsuckers from the mistaken belief that they suck milk from goats (the Latin for goatsucker is Caprimulgus).
Nighthawks have small feet, of little use for walking, and long pointed wings. Their soft plumage is cryptically coloured to resemble bark or leaves. Some species, unusual for birds, perch along a branch, rather than across it. This helps to conceal them during the day. They lay two patterned eggs directly onto bare ground.
They are mostly active in the late evening and early morning or at night, and feed predominantly on moths and other large flying insects.
Nighthawks are similar in most respects to the nightjars of the Old World, but have shorter bills and less soft plumage. Nighthawks are less strictly nocturnal than many Old World nightjars, and may be seen hunting when there is still light in the sky.