Steatornis caripensis

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.

• Biogeographic Regions
• neotropical neotropical
  • native native

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.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest
• rainforest rainforest
• mountains mountains

• Other Habitat Features
• caves

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.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes colored or patterned differently
• female more colorful

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.

• Mating System
• monogamous monogamous

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.

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

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

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.

• Parental Investment
• altricial altricial
• male parental care male parental care
• female parental care female parental care
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female

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.

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.

• Key Behaviors
• arboreal arboreal
• troglophilic
• flies
• nocturnal nocturnal
• crepuscular crepuscular
• motile motile
• sedentary sedentary
• territorial territorial
• social social
• colonial colonial

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.

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• echolocation echolocation
• vibrations vibrations
• chemical chemical

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.

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.

• Primary Diet
• herbivore herbivore
  • frugivore frugivore

• 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.

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.

• 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.

• Positive Impacts
• ecotourism ecotourism

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.

Additional Links

Encyclopedia of Life

Contributors

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

References

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

Hilty, S. 2003. Birds of Venezuela . 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.

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