oilbird, common name for an owllike, cave-dwelling bird, Steatornis caripensis, belonging to the family Steatornithidae. It spends its days in dark caves, maneuvering by means of a batlike sonar device, or echolocator, found in its ears. The oilbird emits a clicking sound at an audible frequency of 7,000 cycles per sec, unlike the bat's cry, which is supersonic. Hence the pulsations of the oilbird can be easily detected by the human ear while the bird is in flight. For night-flying, the bird depends upon its large, highly light-sensitive eyes.
Oilbirds, also called guácharos, are found throughout N South America and on the island of Trinidad. As much as 13 in. (33 cm) in body length, with wingspans up to 3 ft (91 cm), they are rich brown in color with black bars and scattered white spots. They have hooked beaks surrounded by stiff, whiskerlike hairs. The beaks are used to pluck fruit while the bird hovers in the air; it never perches. Oilbirds are also the only nocturnal, fruit-eating birds.
Oilbirds nest in large colonies on high, rocky cave ledges, often a good distance into the cave. The female lays two to four eggs per clutch, which hatch in about 33 days. The naked young are fed on rich, oily fruits and become grotesquely fat, reaching twice the adult weight at their maximum size. They lose this "baby fat" when their feathers begin to grow in. In the past, baby oilbirds were captured, and their fat boiled down for torch oil, hence their name.
Oilbirds are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Caprimulgiformes, family Steatornithidae.