The nocturnal fruit-eater that navigates dark caves using high-pitched clicks like a bat.

Nature · Published 3 October 2026 Swipe more like this →

In short: The oilbird is a biological anomaly: a nocturnal, fruit-eating bird that navigates pitch-black caves using echolocation. While most birds rely on sight, this South American specialist uses rapid clicks to maneuver through narrow caverns. Once harvested for their fat, these birds remain one of nature's most peculiar evolutionary success stories.

The oilbird, or guácharo, is the sole member of its order, Steatornithiformes. Found across northern South America, these birds are unique among avian species for being nocturnal fruit-eaters. While they possess highly specialized eyes with the highest rod density of any vertebrate—allowing them to forage in dim light—they supplement their vision with echolocation. By emitting audible 2 kHz clicks, they can navigate the complex, restricted environments of their cave homes, a trait they share with only a few other birds like certain swifts.

Their lifestyle is defined by a strange duality. Historically believed to be strictly cave-dwellers, recent GPS tracking has revealed that non-breeding individuals spend roughly two out of every three nights roosting in trees. This behavior suggests a complex trade-off: forest-roosting birds face higher predation risks, while those in caves must expend significant energy defending nesting ledges from rivals. These nests, built from droppings on rock shelves, produce chicks that grow remarkably heavy, often weighing 70 to 100 percent more than their parents before fledging.

The bird's scientific name, Steatornis, translates to 'fat bird,' a nod to the historical practice of boiling down chicks for oil. Today, the species is considered stable, with the IUCN estimating a population of 20,000 to 50,000 mature individuals as of 2021. Despite their specialized nature, fossil evidence from the Green River Formation in Wyoming suggests that the family was once far more widespread, with prehistoric ancestors likely consuming similar fruits and spreading seeds across a much larger global range.

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