The order Caprimulgiformes includes four families of birds with not only odd appearances but odd names. Commonly called nightjars, the order is comprised of about 120 species of soft-plumaged and cryptically colored birds including nighthawks, potoos, frogmouths, poorwills, owlet-frogmouths and oilbirds. Resembling strange owls, nightjars lack the talons and strong beak; in fact their feet are so small and weak they often stretch horizontally on the ground or a tree branch to sleep during the day. Most are crepuscular or night-flying birds and many produce strange and haunting sounds.
The family Caprimulgidae includes nightjars, eared-nightjars and nighthawks.
Caprimulgus, the genus of nightjars and whip-poor-wills, derives from the Latin word capra, meaning goat, and mulgere, to milk, referring to an ancient myth that the birds seen flying near goats at dusk were suckling on the goats’ udders, a misconception probably induced by the birds’ uncommonly large mouths.
The Podargidae includes 15 species of frogmouths, found in India, Asia, and Australia. Frogmouths have a large, flattened, hooked bill that looks like a frog’s mouth when it is open. During the day, they stretch out horizontally on tree branches and sleep. They eat insects and small animals like frogs and mice. They often beat their prey against rocks after capturing it. Podargus derives from the Greek word for gout as the weak feet of these birds give them an unusual gait.
The Steatornithidae contains only one species, the Oilbird This species lives only in western and northern parts of South America. It is the only vegetarian of the Caprimulgiformes; it exclusively eats oily fruits, mainly palm. During the day, the Oilbird lives and rests in grottoes and caverns where it also reproduces. Nocturnal, it uses echolocation, much like a bat’s sonar, to navigate. The Oilbird so called because the young birds are so fat that indigenous people and early settlers once collected and rendered them to produce oil for lighting and cooking. (Steatornis means “fat bird.”) Oilbirds spend their days in darkness and awake just before dusk and leave their roosts to feed, using keen nocturnal vision and sense of smell to locate fruit, which they pick from trees while hovering.
The family Nyctibiidae, meaning “night-feeding”, contains seven species of birds distributed in Central and South America called Potoos, after their call, and which occupy the same ecological niches as the Frogmouths. Potoos resemble upright nightjars with proportionately large heads for their body size as well as long wings and tails. Potoos’ typical foraging technique is to perch on a branch and occasionally fly out in the manner of a flycatcher in order to snatch a passing insect.
Most Caprimulgiformes have rictal bristles, modified feathers, that extend out from the sides of the jaw, as do a number of other birds. Once thought to serve as a net or sieve to funnel flying insects into the mouth, rictal bristles have no direct role in insect capture but instead serve as sensory devices to provide information to the bird regarding its flight speed and orientation.