OILBIRD: Steatornithidae

PHYSICAL CHARACTERISTICS

Oilbird plumage (feathers) is the color of cinnamon, and the bird's reddish brown feathers are dotted with white spots. The long tail is colored by faint black bars, lines of color. Males and female birds have similar coloring, and females are slightly smaller than males.

The oilbird is the only member of the Steatornithidae family. While they resemble owls, order Strigiformes, oilbirds belong to the Caprimulgiformes order. Like other families in the Caprimulgiformes order, the oilbird has a large gape, the width of the mouth when it's open.

Birds in the Caprimulgiformes and Strigiformes orders are nocturnal, active at night, and their large eyes provide the strong vision needed to see at night. Both owls and oilbirds have hooked bills, but the owl has sharp claws on its feet. The owl uses these talons (TAL-unz) to capture prey, animals hunted as food. Oilbirds have small feet and eat only fruit.

Oilbirds eat fruit that is rich in fat and oil, which provides the energy needed to fly. When chicks are fed these fruits before they are able to fly, they become very fat, often growing larger than the adults. While adult birds weigh from 13 to 16 ounces (375 to 455 grams), a seventy-day-old oilbird chick weighs approximately 21 ounces (600 grams). As the young bird develops, the parents feed it less often. The combination of less food and growing into adulthood causes the oilbird to lose weight. Oilbirds got their name from the fact that in the past chicks were captured and boiled down in order to make oil.

Adult oilbirds measure 17 to 19 inches (43 to 49 centimeters) in length. The bird has blue eyes and a yellow beak with whisker-like bristles on both sides. The oilbird uses its bill to pluck fruit from trees.

Since oilbirds have short feet, they do not perch or stand on trees. Instead, the bird rests, which is like sitting. At rest, the head of the oilbird is lower than its tail. Furthermore, their feet are so weak that they do very little walking, instead they fly to get from one place to another.

Their wingspan, the distance between the fully spread wings, is approximately 37.5 inches (95 centimeters). The wings are wide and slotted so that the oilbird can fly slowly while carrying loads into the dark caves where they live during the day. At night, oilbirds use their powerful wings to fly as far as 75 miles (120 kilometers) in search of food.

GEOGRAPHIC RANGE

Oilbirds live mainly in South America and are found in the countries of Guyana, Trinidad, Venezuela, Colombia, Ecuador, Peru, Brazil, and Bolivia. Oilbirds also range in the Central American countries of Costa Rica and Panama, and the islands of Tobago and Aruba.

HABITAT

Oilbirds live in caves along coasts and in the mountains. Birds make their homes in areas near coniferous or evergreen forests¸ where trees do not undergo seasonal changes. While generally found in caves, oilbirds also live inside gorges, deep, narrow areas.

DIET

Oilbirds are frugivores, animals that eat fruit. Oilbirds eat the fruits of palm trees, laurel trees, and avocado trees.

BIRDS AS AN OIL SOURCE?

In centuries past, people in Central and South America realized that the fruit-eating birds were a source of oil. People captured the plump nestlings and boiled them to obtain yellow oil. People cooked with the oil and used it to light their lamps. In the twenty-first century, oilbirds became a protected species in many countries, so they are no longer hunted for their oil.

Groups of oilbirds forage at night, looking for food. They fly down, pluck fruit from the trees, and swallow it whole. Oilbirds eat the soft pulp inside the fruit. During the day, birds digest their food and then regurgitate (re-GER-jih-tate) the seeds. Regurgitation is the process of vomiting, removing food in the stomach through the mouth.

BEHAVIOR AND REPRODUCTION

The Spanish name for oilbird is guácharo, meaning "one who cries." Oilbirds can be noisy. If people invade their caves, the birds will shriek or squawk loudly to warn other oilbirds and frighten the invaders. The oilbird family is social, and colonies, groups of birds, live together in caves.

A large cave in Caribe, Venezuela, is said to house about ten thousand oilbirds. A protected population lives in Dunston Cave in Trinidad's Asa Wright Nature Centre. The center tracks the bird population by doing a bird count several times each year. The bird census in November of 1998 was 119 adults. In June of 2003, there were 120 adults, twenty chicks, and two eggs. The following December, the center counted 154 adult oilbirds.

Oilbirds become active at twilight, and the colony flies out at night to forage for food. Birds usually look for fruit in pairs and groups. Their vision is strong enough to hunt for food at night. However, the birds rely on sound to guide themselves inside dark caves.

Oilbirds enter the cave and make clicking sounds at a frequency low enough to be heard by people. They click at the rate of ten to twelve clicks per second, with the number of clicks increasing as oilbirds get closer to an obstacle. Oilbirds know to click faster because they listen to the echo of the click as the sound bounces off surfaces like walls and rocks. Their brain compares the echo with the sound of the original click. The brain analyzes how close the echo is, and the birds adjust their flight so they will not crash into something. This navigation system, called echolocation (eck-oh-loh-KAY-shun), is also used by porpoises, whales, and bats.

During the day, oilbirds roost, rest in caves. Oilbirds are thought to be monogamous (muh-NAH-guh-mus), with a single male and single female bird staying together permanently. The two birds roost together on flat surfaces like ledges.

Oilbirds often breed during the rainy season, but this may vary by location. In Venezuela's Caribe Cave, females lay eggs in April and May. The timing is believed to be connected with the abundance of laurel tree fruit. In Trinidad, the population of nestlings, birds without feathers, is highest in May and June.

Breeding oilbirds build nests far inside caves and away from predators. Nests are usually on ledges located 33 to 66 feet (10 to 20 meters) above the floor of a cave. The oilbird nest resembles a saucer and is made of material including regurgitated seeds and fruit pulp. Birds use their saliva as a glue to hold the nest together.

Female oilbirds lay a clutch of two to four white eggs. Both parents incubate the eggs, sitting on them until they hatch in thirty-two to thirty-five days. The chicks weigh from 0.4 to 0.5 ounces (12 to 15.5 grams). They are born with their eyes closed and have few feathers. Parents feed the chicks fruit, and the young birds become plump. They weigh almost twice as much as adult birds at seventy days old. The nestlings have feathers, but their tails and wings are smaller than adults. At they grow into adulthood, their feathers develop and they lose weight. Young oilbirds leave the nest when they are 110 to 120 days old.

OILBIRDS AND PEOPLE

Oilbirds were once hunted as food or a source of oil. In the twenty-first century, the birds are legally protected in many countries, which means that it is against the law to injure or kill oilbirds in those nations. Furthermore, oilbirds are a tourist attraction. People vacation and visit oilbird caves in places like Caribe, Venezuela, and Trinidad.

CONSERVATION STATUS

Oilbirds are not in danger of extinction, dying out. However, they may become endangered if forests are cut down, since trees provide the only source of food for these fruit-eating birds.

FOR MORE INFORMATION

Web sites:

"Oilbirds." Asa Wright Nature Centre & Lodge. http://www.asawright.org/nature/oilbirds.html (accessed on June 1, 2004).

Querna, Betsy. "Native Son Captures Beauty of Trinidad's 'Eden.'" National Geographic Today. http://news.nationalgeographic.com/news/2001/05/0508_trinidadphotographer.html (accessed on June 1, 2004).

Thomas, Betsy T. "Family STEATORNITHIDAE (OILBIRD)" Handbook of the Birds of the World. Online at http://www.hbw.com/hbw/volume5/famil501.html (accessed on June 1, 2004).