The Oilbird is a large, strange, vegetarian bird that looks rather like an owl, and is only remotely related to other families in its Order Caprimulgiformes (whippoorwills, goatsuckers, and nightjars).

During the day these gregarious birds rest on cave ledges. The nest is a heap of droppings, usually above water - either a stream or the sea, on which 2-4 glossy white eggs are laid which soon become stained brown. These are rounded but with a distinctly pointed smaller end and average 41.2 X 33.2 mm.

The squabs become very fat before fledging, weighing up to half again as much as the adult birds do. They used to be harvested and rendered for oil, whence the name "oilbird". Reportedly the oil is odorless clear, and keeps well. This oil is used mainly in cooking, but also may be used for lamp oil.

Although the Oilbird forages by sight, it is one of only a few birds, and the only nocturnal one, known to navigate by echolocation in sufficiently poor light conditions, using a series of sharp audible clicks for this purpose. It also produces a variety of harsh screams while in its caves which have been likened to those of tortured men. Entering a cave with a light especially provokes these raucous calls; they also may be heard as the birds prepare to emerge from a cave at dusk.

Oilbird

Oilbirds, found in the tropical and subtropical primary forests, are also called guacharos. (The etymology of the American Spanish word guácharo, is from guacho, vagabond, or from Quechua wáhcha, poor person, orphan.)  They have powerful, hooked beaks used to pluck fruit while the bird hovers in the air, never perches when eating. It roosts and breeds in selected caves which have been used by the species for eons. The Oilbird ranges across much of northern South America and along the Andes all the way down to Bolivia. 

Colonies leave their caves at night to fly to fruit-bearing trees. Figs are the most often consumed fruit, although 36 kinds of other fruit, including the fruits of palm and laurel trees, have also been documented. The Oilbird is an important component of the tropical ecosystem because it widely spreads the seeds of digested fruit as guano. The forest depends on these fruit-eaters -- and other animals with similar behavior, such as fruit bats -- to perpetuate its existence.

Like bats, Oilbirds echolocate inside caves, however, once they leave the communal roosts use their huge eyes. Unlike the bat’s cry, which is supersonic, the oilbird emits a clicking sound at an audible frequency of 7,000 cycles per second.  The human ear can easily detect the pulsations of the Oilbird while it is in flight. Its highly light-sensitive eyes, with rows of bristles both above and below protect the eyes make for excellent night vision.

Oilbirds fly rapidly with their widely spaced primary feather tips (like New World vultures), but have the ability to fly slowly and even hover. Radio telemetry studies have shown their normal range per night is 40 kilometers (25 mi), but they have been known to travel as far as 150 kilometers (93 mi) in a single night to find fruit. Studies have shown that all the fruit they eat is spicy or aromatic when ripe, which leads researchers to believe they probably find it by smell.

Oilbirds have cinnamon-brown feathers with white dots. Adults measure from 12 to 18 inches long.

Europeans have known the fabulous Guacharo Cave since 1657, when Franciscan Capuchine Missionaries started their inland penetration south of Cumana.  By 1660, they had established a mission in Caripe called “Santa Maria de Los Angeles del Guacharo”.  Today we know the Chamas Indians inhabited the area many centuries before Columbus crossed the Atlantic, as evidenced by archeological remains. The oldest know description of the cave dates back to 1678, when a Capuchin monk, Fray Francisco de Tauste, described in missionary documents the dense clouds of birds that came out of the Caripe cave at night. He told of tasty oil made from squab, and reported that the local Indians believed the souls of their dead went into this same cave.

The first European explorer of the caves was Bishop Don Francisco de Ybarra y Herrera who explored some 1500 feet of them.  Then, on September 18, 1799, Baron Alexander von Humboldt  explored the cave and Humboldt described the unique bird he saw within as the “oil bird of Caripe”. 

The Cave of "Guacharo" is the biggest cavern in Venezuela.  It was initially decreed a Natural Monument in 1947, and in 1975, was decreed a National Park when the protection area was enlarged to preserve its ecosystem and guarantee the ongoing biological processes of the cavern.  In 1989, an additional 160,000 acres was set-aside at the Mata de Mango, 15 kilometers east of the already protected 25,000 acres, for the Oilbirds at Caripe cave area.  Radio-telemetry had shown the birds of the Caripe cave spent much of their time foraging outside the protected area through the year. In Bolivia, Peru, Trinidad, and Colombia governments have set aside areas near and surrounding Oilbird caves, or are planning to do so. 

William Halliday, M.D. visited the cave in 1978 and reported, “the commercial section consists mostly of one enormous gallery with a winding trail due to massive columns and stalagmites.

A little daylight is present for about 900 feet.  The nests of the guacharos begin about 300 feet inside the cave, although the birds mainly inhabit the Salón Humboldt, where they pass digested food gathered during the night. They kept up a vigorous commentary on our presence, manners, morals, parentage and related topics the entire time the guide and I were in sight.  The birds have a stronger language for their neighbors are territorial and the local air space is continually renegotiated. 

The cave is so high that only occasionally could we see those in flight by our lantern’s light, but a constant click-cluck-cluck of their sonar told us of what was going on in the high shadows.  I obtained some good tapes of the sonar and of the bird’s commentary.

At the end of the guacharo section is a narrow lead, down several levels to a stream that was ankle deep at the time of my visit.  Beyond is a section with several hundred meters of smaller passages and larger rooms with massive speleothems. The commercial section of the cave ends at a duck-under sump.

The sounds are more impressive when the birds leave the site.  It is not like seeing the bats emerge from Carlsbad Caverns or Bracken Bat Cave near San Antonio.  The birds fly much later in the evening than the bats and it is difficult to see them against the darkening sky. What uproar in the cave - all the guacharos are violating everyone’s air space as they prepare to leave for the night.” 

The Cave of Guacharo  has an entrance 70 feet high and 28 feet wide. All visits to the cave are by guided tours, of groups of 10 people. About 3,000 feet of the cave is normally visited, crossing the Salón Humboldt and the Gallery of the Silence (with formations baptized as the Cardón, the Carmen's Virgin, the Guard's Angel) until arriving at the Salón Sublime, where the stalactites and stalagmites formed by the constant action of the water in the rock can be appreciated. Those who want to visit the cave's galleries beyond the usual public access to the next 7.2 miles will need a special authorization from the Inparques.  Some people consider this as one of the most complete cave ecosystems to be found anywhere in South America.