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. Konishi and Knudsen hung plastic discs of different sizes in a flight corridor in 1979: the birds avoided every disc forty centimetres across, avoided some of the twenty-centimetre discs, and collided with the ten- and five-centimetre ones as though nothing were there. That places the working limit at roughly twenty centimetres, enough for cave walls and thick stalactites and no finer. 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.