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Steatornis caripensisoilbird

By Abraham Turner

Geographic Range

The oilbird (Steatornis caripensis) is endemic to South America. Their northern ranges extend through Trinidad, Guyana, and Venezuela. Their southern range primarily runs through the Andes Mountains in Colombia, Peru, Ecuador, and Bolivia. The oilbird is most abundant in caves at the Cueva del Guacharo National Park in Venezuela. They have also been found in Venezuela, residing south along the coastal cordilleras, primary in Tachira, Merida, and Lara. The largest concentration of oilbirds (between 10,000 and 18,000 birds) live in northern Brazil within the Tepui Mountains. The oilbird resides in caves up to 2000 m north the Orinoco River, and 2600 m south of the Orinoco River in Venezuela. Elevational ranges are extremely broad. Oilbirds live in caves near sea level to caves at 3000 m in Columbia, up to 2400 m in Ecuador, and up to 2200 m in Peru. Oilbirds do not typically migrate, but have been recorded straying up to 150 km from their roosting caves in search for food, with reports of birds as far away as 700 km from their nearest known roosting caves. Deforestation in recent years has been resulting in further seasonal movement in search for food. (Bosque, 2002; Hilty, 2003; Hilty and Brown, 1986; Ridgely and Greenfield, 2001; Thomas, 1999; Walker, et al., 2006)

Habitat

The oilbird inhabits neotropical mountain forests and the surrounding lowlands when foraging for food during the night. During the day, oilbirds spend most of their time roosting within mountain caves. In the larger caves in Cueva del Guacharo National Park, the birds reside in a colony, where they are found roosting together by the thousands. However, recent GPS/acceleration loggers implemented by Holland et al. 2009 have shown that oilbirds are only spending some of their days roosting in caves. Large portions of their days are spent in rainforest canopies where they regurgitate seeds. (Hilty and Brown, 1986; Holland, et al., 2009)

  • Other Habitat Features
  • caves
  • Range elevation
    0 to 3000 m
    0.00 to 9842.52 ft

Physical Description

The oilbird is a large bird (body length 43-49 cm beak to tip of tail, 400 g) that looks similar to an oversized nightjar. It’s wingspan ranges from 95-105 cm. Sexual dimorphism is marginal, with males being slightly larger and having more grey in their plumage. The majority of their plumage is a reddish brown with white mottling along the chest, upper wing coverts, and the edges of the undertail. Mottling is present but smaller along head and some primaries. Tails are long with light black barring. Eyes are large, dark brown and reflect red. The large, hooked bill is a rufous brown and has long rictal bristles that often extend past the end of the bill. Wings are large, highly slotted, narrow when in flight, and have a low wing load. The feet, which are located further forward on the body compared to similar species, have light pink toes and tarsi. (Hilty, 2003)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • female more colorful
  • Range mass
    400 (high) g
    14.10 (high) oz
  • Range length
    43 to 49 cm
    16.93 to 19.29 in
  • Range wingspan
    95 to 105 cm
    37.40 to 41.34 in

Reproduction

Oilbirds (Steatornis caripensis) are monogamous and spend the majority of their time in pairs. Courtship takes place at night when the birds are outside of their roosting caves. Two birds circle each other during flight and emit a low clicking noise followed by a harsh “Kurrrr” sound. (Snow, 1960)

Nests are built 10-20 meters off the ground along ledges in large caves. Nests built from regurgitated seed or fruit fibers and their own excrement reach diameters of up to 40 centimeters. Females lay 2-4 eggs, usually 3-5 days apart. Both male and female oilbirds share incubation, brooding, and feeding responsibilities, although females have been shown to incubate up to twice as long and often as males. Incubation lasts between 30 and 35 days. Hatchling development is very slow, typically taking between 90 and 125 days to leave the nest. (Snow, 1960; Wittenberger and Tilson, 1980)

Breeding is moderately synchronized and usually takes place in the rainy season between April and May. Fruiting peaks of Burceraceae, Lauraceae, and Arecaceae coincide with egg laying and specific breeding times in some of the Venezuelan range. In other regions, birds have been found in various breeding stages throughout most of the year. Little is known about copulation (Bosque, 2002; Hilty, 2003)

  • Breeding interval
    Oilbirds breed once yearly.
  • Breeding season
    Breeding is moderately synchronized and usually takes place in the rainy season between April and May.
  • Range eggs per season
    2 to 4
  • Range time to hatching
    30 to 35 days
  • Range time to independence
    90 to 125 days

To keep the eggs and hatchlings warm enough during the incubation and brooding period, at least one bird typically remains at the nest due to low ambient temperatures in the larger caves. During the hatchling development period, the adult oilbirds engorge their young with large amounts of lipid-rich foods allowing them to outgrow their parents by 50% in only 70 days. (Wittenberger and Tilson, 1980)

Lifespan/Longevity

Little is known about lifespan in oilbirds.

Behavior

Oilbirds are frugivorous, nocturnal birds that spend almost all of their time in pairs. Mates preen one another while paired up in their nests. They are highly gregarious during the day, residing along cave ledges in colonies of up to 10,000 birds. Territorial behavior including loud snarls and snoring sounds have been recorded in roosting caves when humans are present. (Roca, 1994; Snow, 1960)

Rudimentary echolocation is used within caves to navigate in complete darkness and communicate with conspecifics. Occasionally, birds will roost outside the cave during the day in rainforest canopies. At night, birds exit the caves in search for food. While foraging outside the cave, intraspecific competition for food resources occurs, usually resulting in broadened foraging ranges. (Brinklov, et al., 2013)

Home Range

Oilbirds stay within their respective caves for the duration of their lives. Home range varies depending on scarcity of food resources.

Communication and Perception

The vocalizations of the oilbird include a variety of harsh screams, screeches, and snoring sounds. They also use rudimentary echolocation to navigate caves in complete darkness. Their screeches typically last around 0.5 seconds and their sonar clicks last 40-50 ms. Both vocalizations use the sternotrachealis muscles, but their echolocation is made possible through their bilaterally asymmetrical bronchial syrinx. Unlike most bats, the frequency of their echolocation is well below 20 hertz, making it audible to humans. While roosting in high densities inside caves, oilbirds must be able to perceive a wide array of reverberations from the cave walls as well as clicks from conspecifics. Echolocation in oilbirds could be a form of communication. In some bat species, it is known that feeding behavior and flight maneuvers change based on echolocation signals emitted by conspecifics. (Brinklov, et al., 2013; Hilty and Brown, 1986; Suthers and Hector, 1985)

Food Habits

Oilbirds (Steatornis caripensis) are strict frugivores that feed entirely on fruits from the avocado family, the Laurel family, and the Palm family. During the breeding season in the spring, Lauraceae is the main source of food due to its high lipid (49.6%) and energy (31.8 kJ/g) content. During the non-breeding season, palms make up the majority of their diet. Hatchling diets are the same as the adults. Both the adults and young swallow the fruit whole, digest the pericarp, then regurgitate the seeds. Digestion and regurgitation takes place during the day when birds are roosting in their caves or rainforest canopies. (Bosque, 2002; Snow, 1960)

Foraging takes place during the night when oilbirds exit the cave, sometimes in groups, in search for fruit trees. Birds have been known to travel up to 25 km per night in search of food and migrate short distances seasonally when food abundance is low. Individual fruits are located with the oilbirds highly adapted nocturnal vision. Olfaction is thought to play a role in locating foraging sites due to the oilbirds thick mucous membranes, highly developed olfactory system, and the strong aroma of Lauraceae and Burceraceae. While foraging outside the cave, intraspecific competition for food resources occurs. This increases their foraging range and aids in seed dispersal to remote land patches. Occasional daytime roosting sites outside the cave are different from foraging sites. Regurgitation of fruit seeds during these daytime roosting periods also increases seed dispersal. (Hilty and Brown, 1986; Snow, 1960)

  • Plant Foods
  • fruit

Predation

Nesting sites built 10-20 meters off the ground along cave ledges and their nocturnal foraging habits prevent predation on oilbirds. It it thought that predation pressures on hatchlings was an evolutionary driver for their nesting behaviors. (Holland, et al., 2009)

Ecosystem Roles

Regurgitation of seeds while roosting in rainforest canopies makes the oilbird one of the most significant seed dispersers in neotropical rainforests. Regurgitation takes place away from foraging sites which allows Lauraceae, Burceraceae, and Arecaceae to be dispersed and germinated in new locations. As deforestation becomes a greater threat in large portions of their range, the oilbirds feeding ecology becomes increasingly important for neotropical forests in South America. (Holland, et al., 2009; Snow, 1960)

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

The oilbird is a highly sought after species for amateur bird enthusiasts in South America. Dunston Cave, one of the most popular caves in the Asa Wright Nature Center, is an important ecotourism destination in northern Trinidad and brings significant economic support to the region. The Cueva del Guacharo National Park in Venezuela also provides excellent opportunities for birders to witness the largest aggregation of oilbirds roosting in one location.

Before their legal protection in the 21st century, oilbird hatchlings were captured and used for lamp oil. Due to the high lipid content in the juveniles diet, they were also a rich source of energy and protein for humans. (Bosque, 2002)

Economic Importance for Humans: Negative

There are no known negative effects of oilbirds on humans.

Conservation Status

Although oilbird populations are experiencing a slight decline, they are listed as ‘least concern’ on the IUCN red list due to their extremely large range (1,040,000 km2) and population size (100,000 - 500,000 individuals). Deforestation does pose a threat due to the highly specialized diet of the oilbird. In some conservation lands and national parks the oilbird is under legal protection. (Bosque, 2002)

Contributors

Abraham Turner (author), Northern Michigan University, Alec Lindsay (editor), Northern Michigan University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

crepuscular

active at dawn and dusk

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

frugivore

an animal that mainly eats fruit

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

1985. The Physiology of Vocalization by the Echolocating Oilbird. Journal of Comprehensive Physiology, Vol 156/Issue 2: 243-266.

Bosque, C. 2002. Steatornithidae: Oilbirds. Grzimek's Animal Life Encyclopedia, 2: 373-376.

Brinklov, S., B. Fenton, J. Ratcliffe. 2013. Echolocation in oilbirds and swiftlets. Frontiers in Physiology, 4/123: 335-341.

Hilty, S. 2003. Birds of Venezuela. Princeton, New Jersey: Princeton University Press.

Hilty, S., W. Brown. 1986. A guide to the birds of Columbia. Princeton, New Jersey: Princeton University Press.

Holland, R., M. Wikelski, F. Kummeth, C. Bosque. 2009. The Secret Life of Oilbirds: New Insights into the Ecology of a Unique Avian Frugivore. PLOS One, 4/12: 8264. Accessed March 21, 2018 at https://doi.org/10.1371/journal.pone.0008264.

Ridgely, R., P. Greenfield. 2001. The birds of Ecuador: status, distribution, and taxonomy.. New York: Cornell University Press.

Roca, R. 1994. Oilbirds of Venezuela: Ecology and Conservation. University of Cambridge: Nuttal Ornithological Club.

Snow, D. 1960. The Natural History of the Oilbird, Steatornis caripensis, in Trinidad.. General Behavior and Breeding Habits, 37/13: 157-184.

Suthers, R., D. Hector. 1985. The Physiology of Vocalization by the Echolocating Oilbird.. Journal of Comprehensive Physiology, 156/2: 243-266.

Thomas, B. 1999. Family Steatornithidae (Oilbird). Barcelona, Spain: Lynx Edicons.

Walker, B., T. Stotz, Pequeno, J. Fitzpatrick. 2006. Birds of the Manu Biosphere Reserve. Peru: Fieldiana: Zoology.

Wittenberger, J., R. Tilson. 1980. The Evolution of Monogomy: Hypothesis and Evidence.. Annual Review of Ecology and Sysematics, 11: 197-232.

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