The Guacharos, Oil Birds or Diablotin (Steatornis caripensis) are a rare species of nocturnal bird which navigates by echo location. Because of their big fluorescent eyes they are sometimes also called blind birds. However, they are not blind, and their sonar makes them see in the dark, which is unique among birds. They can be found in the northern part of South America, in Venezuela and Bolivia for example.
The Guacharo often live in caves, so they are cave lovers or trogloxene. They leave the cave every evening after dark to feed on fresh fruit. They are of a dark grey-blue colour, grow up to a size of 60 cm and a wingspan of 110 cm, and look like a bird of prey.
The oil birds were first described and named by Alexander von Humboldt at the Cueva del Guácharo in Venezuela. He observed the bats, the birds, and the other animals in the cave and described them in his book about this South America journey. He named the birds Fettschwälme, which is the base of the above names in other languages. As this book was sold many times all over Europe, a very early bestseller, the Guacharos became rather famous.
When Alexander von Humboldt visited the cave in 1799 the local monks described to him, how the local Indians hunted the birds for their fat deposits. At midsummer they entered the cave with long poles and destroyed most of the thousands of nests lining the high roof. The young birds were killed and stripped of the layer of fat between their thighs, which was melted in clay pots over fires and filtered to produce a pure, clear, odourless liquid. As superstitious dread prevented the Indians from entering very far into the cave, and then only on an annual basis, the colony managed to survive!