The Oilbird (Steatornis caripensis) is a singular tropical bird, and as such belongs to its own family, the Steatornithidae, which is most closely related to the nightjars (Order Caprimulgiformes). The oilbirds are found in the Amazon and other Neotropical regions, from eastern Panama to Colombia and Venezuela, south to Peru and Bolivia. I took the above photograph in Trinidad and Tobago, off the coast of Venezuela.
Oilbirds are so named because they eat large fruits that are high in oil and protein, especially palm fruits, Lauraceae (same family as avocados), and Burseraceae. The fruits are plucked in flight and swallowed whole, the pericarp is digested, and the seeds are regurgitated (probably they are important seed dispersers, though it is unclear what proportion of the seeds are regurgitated outside the cave). Many of these fruits are aromatic, and there is evidence that oilbirds find them at night using a well-developed sense of smell. Palm fruits are not aromatic but perhaps their shape is easy to recognize.
As you can see in the photo, oilbirds live and breed in caves, like bats. They are gregarious and forage in groups, and form lifelong pair bonds. Also like bats, they can echolocate—the unrelated swiftlets are the only other birds that can—and their echolocation clicks are actually audible to the human ear. Listen in the audio track for the clicking noises, not the screams. They use this to navigate caves and because they forage at night.
The nest is a 15”-wide mound made of paste of regurgitated fruit (home sweet home!). The young grow very slowly because of their high-fat diet and don’t fly until 3-4 months. In fact, the juvenile birds weigh 1.5 times as much as their parents when 10 weeks old! The genus name Steatornis means “fat bird.” I haven’t read any mention of how they lose the weight.
It has been reported that native Venezuelans captured these fat young birds and boiled them down to produce oil for cooking and lighting. Another version of this story said that natives would put the birds on a stick and use them for torches! Wow.
References:
Kenefick, Restall, and Hayes, Field Guide to the Birds of Trinidad and Tobago (Yale University Press, 2008)
J. Kricher, A Neotropical Companion (Princeton University Press, Princeton, ed. 2, 1997)
Snow, D.W., The natural history of the Oilbird, Steatornis caripensis, in Trinidad, W. I. Part 2. Population, breeding ecology, and food. Zooligica, 1962. 47: p. 199-221.
Map of Life - “Echolocation in birds: oilbirds and swiftlets”
http://www.mapoflife.org/topics/topic_436_Echolocation-in-birds-oilbirds-and-swiftlets/
May 21, 2012
