The clicks fall around 2 kilohertz, well within human hearing, and are produced in rapid bursts as the bird flies through cave passages. Alexander von Humboldt described the colonies in 1799, and Donald Griffin demonstrated the echolocation experimentally in 1953, shortly after establishing the phenomenon in bats.
The resolution is limited by wavelength. Because oilbird clicks are far lower in frequency than bat calls, the smallest obstacle the system can resolve is on the order of centimetres rather than millimetres. Experiments in which birds flew past discs of varying size found they avoided large obstacles but collided with small ones. Echolocation therefore handles the cave; outside, the bird relies on very large eyes and an acute sense of smell to find ripe fruit.
The name comes from use rather than biology. Nestlings accumulate heavy fat deposits from a fruit diet, and they were historically boiled down for oil.