a web page by Don Roberson |
OILBIRD Steatornithidae |
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 The Oilbird is a large, strange, vegetarian nightbird only remotely related to other families in the Order Caprimulgiformes. It roosts and breeds in selected caves that are used by the species for eons. Brad Schram took this nice shot of several roosting Oilbirds (left) at a traditional site on Trinidad. Oilbird colonies in Trinidad are permanent and the birds sedentary; the only movement is post-breeding dispersal. It appears the individual birds may use the same roosting spots year-after-year. Compare Brad Schram's photo of a roosting spot in Dunston Cave, Trinidad, with my own Oilbird photo (below) showing a roost spot in that same cave, taken almost 7 years later. Flash photography is not permitted here, so these are hand-held shots in the beam of a flashlight. Despite differences in years and techniques, the photos may show pretty much the same spot in the day-roost. |
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| As a species, Oilbird is resident locally on Trinidad and across much northern South America and down the Andes all the way to Bolivia. It is a bird of tropical and subtropical primary forests. Colonies roost and breed in caves. The largest colony reported is at Caripe, Venezuela ((10,.000–18,000 birds). individuals). At night they leave the caves to fly to fruiting trees. Figs are often consumed but the Trinidad population has been documented eating over 36 kinds of fruit. The seeds of these fruit are spread widely after passing through the bird's system — Oilbird is thus an important component of the tropical ecosystems. Oilbird evolved long ago. There are fossils going back nearly 50 million years from the Green River Formation in Wyoming. They may have once been widely distributed in the early radiation of birds across the Northern Hemisphere (Thomas 1999). |
At night, oilbirds fly fast with primary tips widely spaced (like New World vultures) but have the ability to fly slowly or even hover. They can range quite a distance in search of fruit. Radio telemetry studies have shown their normal range per night is 40 kms (25 mi) but they have traveled as far as 150 km (93 mi) in a single night. They may find fruit by smell. Studies have shown that all the fruit they eat is spicy or aromatic when ripe. The In the Andes some caves may be used only in the breeding season. Everywhere they have been studied nesting is initiated at the end of the dry season. This can be as early as March (or as late as July in Trinidad). I visited an Oilbird cave in July 1975 in the western Andes of Colombia but no birds were present that day. Interestingly, post-breeding dispersants have been found away from South America, with records to various Caribbean islands which have no breeding populations (e.g., the Netherlands Antilles) and in Central America north to Costa Rica (Bosque 1988). |
The feathers of an Oilbird are unique and unlike any other bird, but few folks would know this. I have heard a story — perhaps apocryphal — about an Oilbird feather and a birding trip to Attu Island at the end of the Aleutian chain in Alaska. Indeed, it is so far out there that the date line has a huge kink just to keep Attu in the same day as the rest of the United States. For a couple decades expeditions were mounted to this remote barren island in spring in hopes of finding Siberian vagrants. The hope was to find first North American records among these migrants. Attours (the organizing company) always had several "big name" leaders along. One year, the story goes, someone brought an Oilbird feather along surreptitiously and arranged for one of the less experienced birders on the island to "find" it in the field and bring it in to dinner. When she did so, the feather was passed around from big name to big name and nobody had any clue what it was — except that it "must" be a first North American record, whatever it was. Or at least that's how it went until the feather reached Laurence C. Binford, professional ornithologist and at that time the director of the California Academy of Sciences. Laurie said calmly "oh, its an Oilbird" and there went the whole practical joke. Damn ornithologists . . . . |
Photos: The colony of Oilbird Steatornis caripensis was photographed by Brad Schram on 29 Feb 2000 at Dunston Cave, Asa Wright Nature Center, Trinidad (top photo); my own photo of part of the colony (middle shot) was at the entrance to that same cave on 25 Dec 2006. The photo of our guide and Dunston Cave sign was on the way down to the cave that day [incidentally, at that time Oilbird was my last bird family under traditional taxonomies, and thus completed the set. That proved to be a short-lived accomplishment. New research and DNA evidence would elevate dozens of new bird families after 2006. I still don't have them all, some 14 years later . . . ]. The final Oilbird photo is from a roadside culvert in San Martîn province, Peru, on 17 Nov 2014. All photos © Don Roberson, except that credited to © Brad Schram, and used with permission; all rights reserved. Family Book: There is no single book devoted solely to the Oilbird. The family is covered in the Nightjars: A Guide to the Nightjars, Nighthawks, and their Relatives book in the Pica Press series (Cleere 1998) and in the Nightjars & Allies: the Caprimulgidae book in the Oxford Press series (Holyoak 2001). Reviews of both books are on my Nightjar family page. An excellent introduction to the family, with several impressive photos, is in Vol. 5 of the Handbook of the Birds of the World (Thomas 1999). Literature cited:
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Oilbirds echo-locate (like bats) inside caves but use their huge eyes once they leave the communal roosts. They apparently have excellent night vision. Rows of bristles protect the eyes both above and below. Because flash photography has (very properly) been forbidden at well-know caves, my photography efforts are blurry and don't show detail well. This effort (right) was of a colony in a culvert along a paved road in San Martîn province, Peru. It may show an adults with a youngest.
Pairs are monogamous on a long-term basis. The female lays 1-3 eggs and these hatch in about a month. It may take another six weeks to fledge the youngster which has no distinct juvenal plumage. Very young birds are very fat and full of oil; the original name comes from these babies. As we stood at the big explanatory sign near Dunstan Cave in Trinidad (left), our guide explained some rather gruesome uses for fat, oily baby oilbirds in traditional cultures. Fortunately, many caves are now protected.