Oil Bird
Detail about Oil Bird:
The Oilbird, locally known as the guacharo, is a bird species found in the northern areas of South America including the Island of Trinidad. It is the only species in the genus Steatornis and the family Steatornithidae. In truth, it's not quite fair to put the Oilbird in such dubious company-the guacharo, as the bird is known in its native South America, actually has a lot going for it, including the story of its brush with none other than Alexander von Humboldt, famed Prussian naturalist. In 1799, not long into his Latin American expedition, Humboldt led his outfit into the low-lying Caripe mountains of Eastern Venezuela, where they briefly stayed at a Capuchin mission. During their visit, the monks talked Humboldt's ear off about a nearby cave that was occupied by thousands of nocturnal birds. So he decided to see it for himself. And this bird scientific name is Steatornis caripensis.
Description:
This is a large, slim bird at 40–49 cm (16–19 in), with a wing span of 95 cm (37 in). It has a flattened, powerfully hooked, bill surrounded by deep chestnut rictal bristles up to 5 centimetres (2.0 in) long. The adult weighs 350–475 g (12.3–16.8 oz) but the chicks can weigh considerably more, at up to 600 grams (21 oz), when their parents feed them a good deal of fruit before they fly. The feathers of the oilbird are soft like those of many nightbirds, but not as soft as those of owls or nightjars, as they do not need to be silent like predatory species. The oilbird is mainly reddish-brown with white spots on the nape and wings. Lower parts are cinnamon-buff with white diamond-shaped spots edged in black, these spots start small towards the throat and get larger towards the back. The stiff tail feathers are a rich brown spotted with white on either side.
The feet are small and almost useless, other than for clinging to vertical surfaces. The long wings have evolved to make it capable of hovering and twisting flight, which enables it to navigate through restricted areas of its caves. For example, the wings have deep wingtip slotting, like New World Vultures, to reduce the stalling speed, and the wings have a low aspect ratio and low wing-loading, all to make the oilbird capable of flying at low speeds.
The eyes of oilbirds are highly adapted to nocturnal foraging. The eyes are small, but the pupils are relatively large, allowing the highest light-gathering capacity of any bird (f-number of 1.07). The retina is dominated by rod cells 1,000,000 rods per mm2, the highest density of any vertebrate eye, which are organised in layers, an arrangement unique among birds but shared by deep-sea fish. They have low numbers of cone cells, and the whole arrangement would allow them to capture more light in low light conditions but probably have poor vision in daylight.
Although they have specially adapted vision to forage by sight, they are among the few birds known to supplement sight by echolocation in sufficiently poor light conditions, using a series of sharp audible clicks for this purpose. The only other birds known to do this are some species of swift.
In addition to clicks used for echolocation oilbirds also produce a variety of harsh screams while in their caves. Entering a cave with a light especially provokes these raucous calls; they also may be heard as the birds prepare to emerge from a cave at dusk.
Distribution and Habitat:
The oilbird ranges from Guyana and the island of Trinidad to Venezuela, Colombia, Ecuador, Peru, Bolivia and Brazil.They range from sea-level to 3,400 m (11,200 ft). The species has highly specific habitat requirements, needing both caves to breed in and roost in frequently, and forest containing fruiting trees. Where suitable caves are absent oilbirds will roost and breed in narrow gorges and grottos with suitable rock shelves.
One such colony in Ecuador held a colony of a hundred birds in a canyon with ledges protected by vegetation. Some smaller caves and gorges are used only for roosting. While it was once thought that oildbirds always or nearly always roosted in caves, canyons or gullies, researchers placing GPS trackers on non-breeding birds found that they regularly roost in trees in the forest as well as in caves.
It is a seasonal migrant across some of its range, moving from its breeding caves in search of fruit trees. It has occurred as a rare vagrant to Costa Rica, Panama and Aruba. The Guacharo Cave (Oilbird Cave), in the mountainous Caripe district of northern Monagas, Venezula, is where Alexander von Humboldt first studied the species.
Behaviour:
Oilbirds are nocturnal. During the day the birds rest on cave ledges and leave at night to find fruit outside the cave. It was once thought that oilbirds only roosted in caves, and indeed never saw daylight, but studies using GPS/acceleration loggers found that non-breeding birds only roosted in caves or other rock shelters one night in three, the other nights roosting in trees.
The scientists responsible for the discovery also found that birds roosting in caves were highly active through the night, whereas birds roosting in the forest were far less active. They hypothesised that each environment carried costs; birds roosting in the forest were more vulnerable to predators and birds roosting in caves expended considerable energy competing with rivals and defending nesting and roosting ledges.
Breeding:
Oilbirds are colonial cave nesters. The nest is a heap of droppings, usually above water—either a stream or the sea—on which 2–4 glossy white eggs are laid which soon become stained brown. These are rounded but with a distinctly pointed smaller end and average 41.2 millimetres (1.62 in) by 33.2 millimetres (1.31 in). The squabs become very fat before fledging, weighing around a third more than the adult birds.
Oil Bird Video:
Oil Bird Basic Information:
Kingdom: Animalia.
Class: Aves.
Phylum: Chordata.
Order: Caprimulgiformes.
Family: Steatornithidae.
Genus: Steatornis.
Species: S. caripensis.
Binomial Name: Steatornis caripensis.
Higher Classification: Steatornis.
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