The order Caprimulgiformes is known as nightjars and "nightjar" is also the name of the largest family in the order. An order consists of animals with similar characteristics. Caprimulgiformes have large heads, and their large eyes help them see at night. Also large is the gape, the width of the mouth when open. Around the mouths of some birds are whisker-like bristles. The birds have short legs, and many birds have one toe on each foot that points backward, forward, or away from the foot.
Caprimulgiformes have plain plumage. Adults' feathers are brown, gray, brownish yellow, and rufous, a reddish brown. Plumage is patterned, and this protective coloration helps Caprimulgiformes blend in with trees and hide from predators. Members of this order are also known as night birds because they are nocturnal, active at night.
The nightjar family, Caprimulgidae, consists of nineteen genera and seventy-seven species. Birds range in length from 6 to 16 inches (15 to 40 centimeters) and weigh from 0.7 to 6.6 ounces (20 to 188 grams). Members of this family have long wings and tails. They do not have bristles around their mouths. Furthermore, on the middle toe is a claw that is serrated, segments of the claw resemble the teeth of a comb.
The oilbird family, Steatornithidae, has one genus and one species. The birds have hooked bills and are about 17 to 19 inches (43 to 49 centimeters) long. They weigh from 13 to 16 ounces (375 to 455 grams). They are similar to nightjars, and have long wings and tails.
The frogmouth family, Podargidae, consists of two genera and thirteen species. The family name comes from the frogmouth's huge gape and the large beak, which resemble the mouth of a frog. Birds range in length from 7.5 to 24 inches (19 to 60 centimeters) and weigh from 1.5 to 23.6 ounces (43 to 670 grams). Wings and tails are rounded.
The owlet-nightjar family, Aegothelidae, is sometimes called the owlet-frogmouth family. The family consists of one genus and eight species. Owlet-nightjars range in length from 7 to 12 inches (18 to 30 centimeters) and weigh from 1 to 3.5 ounces (29 to 98 grams). Birds' eyes face forward, and the gapes are as wide as birds' heads. Owlet-nightjar wings and tails are long.
The potoo family, Nyctibiidae, consists of one genus and seven species. Birds range in length from 8 to 23 inches (21 to 57 centimeters) and weigh from 1.6 to 2.2 ounces (46 to 624 grams). Birds resemble frogmouths, but are thinner and have smaller bills. Wings and tails are long.