The Oilbird: Is This Thing Even a Bird?

You know the type: They go out after sundown and return again in the morning, and regurgitate whatever they may have ingested during the night. Then they sleep all day and whine at the tiniest sliver of light. They’re almost never caught alone, preferring to gather in large, single-minded groups. Their attempts to grow facial hair are pitiful, but they keep on trying. And they’re always thinking about food. That’s right: I’m talking about Oilbirds (Steatornis caripensis), the only nocturnal, fruit-eating birds in the world! (Other acceptable answers include “my college roommate” or any combination of Greek letters.)

In truth, it’s not quite fair to put the Oilbird in such dubious company—the guácharo, as the bird is known in its native South America, actually has a lot going for it, including the story of its brush with none other than Alexander Von Humboldt, famed Prussian naturalist. In 1799, not long into his Latin American expedition, Humboldt led his outfit into the low-lying Caripe mountains of eastern Venezuela, where they briefly stayed at a Capuchin mission. During their visit, the monks talked Humboldt’s ear off about a nearby cave that was occupied by thousands of nocturnal birds. So he decided to see it for himself.

A few days later, members of an indigenous tribe guided the Humboldt expedition up a small river and into the mouth of the cave. The waning light soon forced them to ignite their torches and a distant squawking grew louder as they proceeded into the cave, where “the shrill and piercing tones of the guácharo reverberate from the arched roof, and echo repeats them in the depths of the cavern,” reported Humboldt. His guides held up their torches to reveal the source of the commotion, which emanated from thousands of funnel-shaped nests glued to the roof of the cave. Humboldt and his crew fired their guns haphazardly into the shadows, and managed to bag two specimens. Then they retreated back into daylight to examine them, finding chestnut colored birds with a hooked beak surrounded on both sides by long, whisker-like hairs.

Thus was the Oilbird discovered by the European scientific world. But Venezuela’s indigenous people had long been well acquainted with the birds, and in particular the plump baby guácharo, which are rich with precious fat that could be used for everything from flavoring food to fueling those torches. Each year, during what they called the oil-harvest, they hiked into the cave and used poles to destroy the nests, killing baby guácharo by the thousands, and then rendered their fat into earthen pots. Fortunately for the guácharo (as a species, if not as individuals), the people believed the souls of their ancestors dwelled in the deepest recesses of the cave, and refused to disturb them, which meant that only the birds closer to the mouth of the cave met the unfortunate fate of becoming torch fuel.

At the time, Humboldt knew he was dealing with a species previously unknown to the scientific world, and a weird, cave-dwelling one at that. What he didn’t know about were all the cool tools the Oilbird has developed to maneuver a world without light. For example, their retinas pack one million rods per millimeter—the highest rod density recorded in any vertebrate—which allows their eyes to take in more light than any other bird’s. And those whiskers, pathetic looking though they might be, actually serve a purpose, providing additional sensory cues that help the Oilbird get around, not unlike many mammals. 

But the oilbird’s most impressive adaptation might be its ability to maneuver within its cavern using echolocation. Unlike bats, which call at a frequency too high for human detection, Oilbirds emit a series of audible-to-humans clicks that ricochet off upcoming obstacles, providing a map of the terrain ahead. How can Oilbirds keep track of their own clicks with so many other birds in the colony? Each Oilbird clicks at a slightly different frequency.

So that’s the Oilbird, and while they may have a few things in common with your typical frat boy, it turns out there are numerous other, more favorable comparisons to be made: They live in caves, like bats; use their whiskers to feel around in the dark, like mice; and rely on sonar to get around, like dolphins. Or, you could just drop the comparisons altogether and see the Oilbird for the totally unique species that it is.

Oh, and one last thing: they’re monogamous. I’d like to see your average frat boy manage that.