The oilbird, or guacharo, is not a morbidly obese bird. It’s called “the whale of the air” because like its larger, ocean-dwelling brethren, it contained oil—oil that was harvested yearly, and which lit lamps and greased up South American society.
The oil comes from the oilbird’s special diet as a chick. Adult oilbirds only weigh about 300 to 450 grams, but the chicks weigh 600 grams. That’s because the adults stuff their chicks with fruit from the oil palm, which is exactly as fatty as it sounds. This makes the chicks balloon up as much as they can and gives them a nice cushion of fat before they start flying and leave the nest. This makes the nearly adult chicks little balls of useful fat—a fact which was not lost on the people living in the northern parts of South America. Wherever oilbirds nested they were hunted for their oil, which was used in cooking, general lubrication of tools and fabrics, and in lamps.
The most famous hunt occurred yearly in Cueva del Guacharo. The cave was huge, extensive, and a traditional nesting place for the oilbirds, which occupied the cave by the tens of thousands. A select group of people would venture into the cave every year, carefully navigate around, and “harvest” thousands of the giant, flightless chicks. The chicks would be killed and essentially “melted down” into oil that would keep for over a year, and be used to light the harvester’s town. When missionaries and monks joined the town, they insisted that first pick of the oil go to them, so they could light sacred lamps in the church they set up. According to some, they also insisted the rest of the oil go to them as well, lighting up their houses and kitchens—though the monks denied it and said they paid for all the oil except the oil used in the church itself.
Because the oil from the oilbird has to be harvested in small bundles, rather than large lumps, it never became a widespread resource the way whale oil did. Still, it wasn’t replaced until synthetic and vegetable oils gained popularity worldwide.