Oilbird

The Oilbird is one of the most unusual birds in the world: a nocturnal, colonial cave-dweller that is entirely fruit-eating, an exceedingly rare combination among birds. It is the only member of its family, Steatornithidae, and its closest relatives are the nightjars and potoos.

Adults are reddish-brown with fine black barring and scattered white spots on the wings and tail, giving a mottled, almost hawk-like appearance in flight. The bird has a strongly hooked bill fringed with stiff bristles, large dark eyes adapted for near-total darkness, and long wings suited to weaving through cave passages and dense forest canopy alike.

Oilbirds nest deep inside caves in large, noisy colonies, and their Spanish name 'guácharo' (wailer) reflects the eerie chorus of screams, clicks, and grunts that echo through their cave roosts.

Key field marks

• Reddish-brown plumage finely barred with black and dotted with small white spots
• Strongly hooked, bristle-fringed bill unlike any songbird
• Long wings and tail giving a hawk-like flight silhouette
• Large eyes reflecting red-orange in torchlight
• Found in dense flocks inside caves, unlike any other bird

Similar species

No other bird shares its combination of nocturnal habits, cave-roosting, and fruit diet. In flight it can superficially recall a large falcon or a potoo, but its cave colonies and distinctive clicking, screaming calls make identification unmistakable once its behavior is observed.

Habitat

Oilbirds roost and breed colonially in deep, dark limestone caves and rocky crevices, sometimes many kilometers from the caves' entrances. They forage at night in humid lowland and montane forest, seeking out fruiting palms and laurel trees.

Range

The species occurs from Panama and Trinidad through the Andean countries of Colombia, Venezuela, Ecuador, Peru, and Bolivia, with the largest and best-known colonies in Venezuela and Trinidad's Dunston Cave.

Migration

Oilbirds are largely sedentary around their cave roosts, though individuals may fly considerable distances each night, and occasionally over 100 km, to reach productive fruiting trees.

Behavior

Oilbirds are the only known nocturnal, echolocating fruit-eating bird. In the total darkness of their cave roosts they navigate using rapid, audible clicks that bounce off cave walls, a form of echolocation similar in principle to that used by bats, though coarser in resolution.

Voice

Colonies produce a constant, unsettling chorus of harsh screams, growls, and clicking calls that echo loudly through cave chambers, audible well outside the cave mouth.

Feeding

They leave their caves after dark to forage on the fruit of oil palms, laurels, and other lipid-rich trees, plucking fruit in flight without landing and sometimes flying long distances between roost and feeding grounds.

Nesting and breeding

Oilbirds nest colonially on ledges deep within caves, building a mound of regurgitated fruit pulp and seeds. Chicks grow extremely fat on the rich fruit diet, historically leading local people to render oil from nestlings, which gave the species its common name.