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Oilbird

life science Maturity 5-7 Next article →

The oilbird, known scientifically as Steatornis caripensis, is a highly specialized bird found in northern South America. It inhabits regions including Venezuela, Colombia, Ecuador, Peru, Bolivia, Brazil, Guyana, and the island of Trinidad. These birds are unique because they are the only nocturnal flying birds in the world that eat only fruit. This diet makes them specialist frugivores, meaning they focus on specific types of food. They primarily forage for the fruits of the oil palm and various tropical laurels. Because they occupy such a specific ecological role, they are classified in their own order, Steatornithiformes.

Steatornis caripensis MHNT ZON STEA 1
Steatornis caripensis MHNT ZON STEA 1

To navigate the darkness, the oilbird uses two distinct biological mechanisms. First, it possesses highly adapted eyes designed for nocturnal foraging. Their small eyes have relatively large pupils, which provides the highest light-gathering capacity of any bird, with an f-number of 1.07. The retina contains a massive density of rod cells, reaching 1,000,000 rods per mm2. This arrangement is unique among birds and is similar to the eyes of deep-sea fish. Second, the oilbird uses echolocation to supplement its vision in very poor light. They emit high-pitched clicking sounds at approximately 2 kHz. These clicks allow them to navigate through tight cave spaces, a trait they share with a few species of swift.

Steatornis caripensis MHNT ZON STEA 1
Steatornis caripensis MHNT ZON STEA 1

The physical appearance of the oilbird is built for its specific environment. An adult bird typically weighs about 1 kilogram, but its chicks can grow much larger. These squabs can weigh up to 1.3 kilograms, which is a third more than the adults. They have a large wingspan and long wings designed for hovering and twisting flight. This maneuverability is essential for navigating restricted areas within caves. Their feathers are reddish-brown with white spots on the nape and wings. The lower parts of their bodies are cinnamon-buff with white diamond-shaped spots edged in black. They also possess a powerful, hooked beak surrounded by chestnut rictal bristles.

Steatornis caripensis MHNT ZON STEA 1
Steatornis caripensis MHNT ZON STEA 1

Historically, the oilbird has a complex relationship with humans. Its common name comes from a practice where people captured chicks and boiled them to produce oil. This connection is also reflected in its scientific name, Steatornis, which means "fat bird." This refers to the significant fatness of the chicks. In some regions, they are known by indigenous names like "guácharo." In Trinidad, they were sometimes called "diablotin," which is French for "little devil." This name likely refers to their loud, harsh screams, which some have compared to the cries of tortured men.

Steatornis caripensis MHNT ZON STEA 1
Steatornis caripensis MHNT ZON STEA 1

The fossil record provides clues about how these birds have changed over time. In 1987, researcher Storrs Olson described the first fossil oilbird from the Green River Formation in Wyoming. This prehistoric species, named Prefica nivea, was likely different from modern oilbirds. It probably did not live in caves or use hovering flight. However, fossils of the same fruit-bearing plants have been found in that same formation. This suggests that ancient relatives of the oilbird may have eaten similar fruits and helped spread seeds much like they do today. Other prehistoric species have also been discovered in France from the Upper Eocene period.

Steatornis caripensis MHNT ZON STEA 1
Steatornis caripensis MHNT ZON STEA 1

Oilbirds have very specific habitat requirements for breeding and roosting. They are colonial nesters that build nests out of heaps of droppings, often above water like streams or the sea. They lay 2 to 4 glossy white eggs that eventually become stained brown. While they are famous for living in caves, recent research has changed our understanding of their behavior. Scientists using GPS trackers discovered that non-breeding birds do not always stay in caves. They found that these birds only roost in caves or rock shelters about one night out of every three. On other nights, they regularly roost in trees within the forest.

Steatornis caripensis MHNT ZON STEA 1
Steatornis caripensis MHNT ZON STEA 1

Conservation efforts are important for protecting these unique birds and their habitats. Large populations exist in protected areas, such as the Cueva del Guácharo National Park in Venezuela. Some estimates suggest there may be 15,000 or more birds living in that single location. Other notable colonies exist in Colombia, Ecuador, and Trinidad, where the Asa Wright Nature Centre houses about 200 nesting pairs. Currently, the IUCN red list classifies the oilbird as "Least Concern." However, researchers have noted that their populations are decreasing. Protecting the forests and caves they rely on is vital for their continued survival.

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