Nombre en español: Guácharo

Nombre en ingles: Oilbird

Nombre científico: Steatornis caripensis

Familia: Steatornithidae

Foto: Gilberto Collazos/Juan Ochoa/Diego Rivera/Jorge Muñoz/Rodrigo Gaviria/Luis Felipe Quintero/Carlos Martinez

Canto: Andrew Spencer

El guácharo (Steatornis caripensis), también conocida como ave de las cavernas o pájaro aceitoso (como en latín, steatornis, o en alemán, Fettschwalm y en inglés, oilbird), es una especie de ave caprimulgiforme de la familia Steatornithidae propia de Sudamérica.

Es la única especie del género Steatornis y de la familia Steatornithidae, y la única ave frugívora nocturna del orden, y una de las pocas aves, y la única nocturna, que navegan por ecolocación en condiciones de baja luz. Esta ave, provista del mecanismo de ecolocación y un potente olfato, se alimenta en la noche de una gran variedad de frutas, lo que la hace casi única.

Mide de 40 a 49 cm y pesa de 350 a 485 g. La hembra es más pequeña que el macho. Esta ave presenta pico fuerte y ganchudo comprimido lateralmente, vibrisas prominentes y fuertes, alas largas y agudas, iris café y patas débiles de color rosa. Por encima es de color castaño marrón con gran cantidad de puntos blancos con bordes negros en las cobertoras alares, en las plumas primarias externas, en las plumas secundarias y rectrices. Por debajo es de color ante canela con puntos blancos más pequeños en forma de diamante. Su cola es larga y gradada estrechamente barrada de negro. Los volantones son similares a los adultos.

Descubrimiento

El guácharo fue descrito por Alexander von Humboldt durante su viaje a Suramérica en 1799. Lo observó en la Cueva del Guácharo, en Caripe (Venezuela). El nombre científico de la especie, Steatornis caripensis, significa «ave aceitosa de Caripe»). La Cueva del Guácharo es el lugar más significativo del Parque nacional El Guácharo.

Historia natural

Vive en colonias en el interior de profundas cavernas. Durante el vuelo nocturno fuera de las cavernas, arranca sus principales alimentos (nueces de palma) con su poderoso pico ganchudo. Mientras vuelan en cavernas oscuras, los guácharos emplean un sistema de orientación por ecos similar al sonar, produciendo “cliqueos” audibles de frecuencia de 2000 ciclos por segundo. Se puede oír fácilmente cuando el pájaro esta en vuelo. A las 10 semanas de nacidas, las crías tienen 50 por ciento más de peso que sus padres. El cuerpo de los polluelos está lleno de grasa y se sabe que éstos comen un cuarto de su peso cada noche.

Distribución

Los guácharos se encuentran en el Parque Nacional El Guácharo ubicado en Venezuela, estado Monagas, Caripe. Hasta ahora la cueva donde se ubican estas aves no ha sido explorada en su totalidad, debido a los ríos que se pueden observar en su interior, no se sabe con certeza si la cueva posee otra entrada o hasta donde se extiende.

También es una especie representativa de el Huila, Colombia en el PPN de los Guácharos.En el corregimiento la Danta, municipio de sonsón al oriente del departamento de Antioquia, se encuentra la caverna la Gruta,localizada en una cuchilla kárstica. Allí habita una gran colonia de estas aves,tiene una extensión de 220 mts, atravesados en su totalidad por un riachuelo de cristalinas y refrescantes aguas. El hotel la caverna ofrece recorridos por las cuevas. En Ecuador, en la provincia de Morona Santiago, en una cueva denominada «Cueva de los Tayos», debido a que en esta región se conoce a estas aves como Tayos.

En Perú existe la Cueva de los Guácharos cerca del pueblo de Sol de Oro, en la provincia de Rioja.

También se encuentran en Bolivia, en la localidad de Colomi, Departamento de Cochabamba en la región de Tablas Monte en el cañón conocido como «Tuta Wallpa»

Reproducción

En Colombia en el Parque Nacional Natural Cueva de los Guácharos y el Parque Nacional Puracé, su temporada de cría se extiende desde diciembre hasta junio. Es un ave monógama que anida colonialmente en escarpes rocosos o en cuevas y usan sus nidos en años consecutivos. Su nido tiene forma de cono o plato de 20 a 45 cm de alto y 25 a 38 cm de ancho en la parte superior. Consiste es un cúmulo de excremento, pulpa y semillas regurgitadas que sujeta con su saliva sobre una repisa en una pared rocosa. El tamaño de su postura es de 2 a 4 huevos de color blanco los cuales incuban de 32 a 35 días. Ambos padres participan en todas las labores concernientes a la reproducción. Las crías crecen muy lentamente debido a que son alimentadas únicamente con frutos y adquieren el peso de un adulto cerca del día 88 al día 125 después de la eclosión. Las crías generalmente no retornan a la cueva natal.

Comportamiento

Es un ave nocturna y gregaria. Durante la noche se mueve hasta 150 km desde los lugares de reproducción o descanso hasta los lugares de forrajeo. Captura los frutos al vuelo los traga enteros y consume únicamente el pericarpio regurgitando las semillas intactas. Fuera de época reproductiva migra a regiones alejadas de las cavernas en búsqueda de alimento. Estas aves son capaces de navegar por ecolocación pero localizan los frutos mediante olfato y en el caso de plantas no aromáticas mediante la visión.

Alimentación

Se alimenta exclusivamente de frutos, principalmente los de palma durante todo el año y de plantas aromáticas temporalmente. En su dieta se han registrado frutos de algunas especies de las familias Lauraceae, Burseraceae, Myrtaceae y Araliaceae. Las lauráceas constituyen una de las familias más importantes en su dieta debido a sus periodos de fructificación bien definidos y a su alto contenido de lípidos y grasas en sus frutos.

Oilbird

The oilbird (Steatornis caripensis), locally known as the guácharo, 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. Nesting in colonies in caves, oilbirds are nocturnal feeders on the fruits of the oil palm and tropical laurels. They are the only nocturnal flying fruit-eating birds in the world (the kakapo is flightless). They forage at night, with specially adapted eyesight. However they navigate by echolocation in the same way as bats, one of the few birds to do so. They produce a high-pitched clicking sound of around 2 kHz that is audible to humans.

Taxonomy and etymology

Oilbirds are related to the nightjars and usually placed with these in the order Caprimulgiformes. However, the nightjars and their relatives are insectivores while the oilbird is a specialist fructivore, and it is sufficiently distinctive to be placed in a family (Steatornithidae) and suborder (Steatornithes) of its own. Some research indicates that it should even be considered a distinct order (Steatornithiformes).

The caripensis of the binomial name means «of Caripe», and Steatornis means «fat bird», in reference to the fatness of the chicks. The oilbird is called a guácharo or tayo in Spanish, both terms being of indigenous origin. In Trinidad it was sometimes called diablotin (French for «little devil»), presumably referring to its loud cries, which have been likened to those of tortured men. The common name «oilbird» comes from the fact that in the past chicks were captured and boiled down in order to make oil.

The fossil record of the family suggests that they were once more widely distributed around the globe. The first fossil oilbird was described by Storrs Olson in 1987 from a fossil found in the Green River Formation in Wyoming. The species, Prefica nivea was probably not adapted to hovering flight or living in caves, unlike the oilbird. Some of the same families and genera of plants the present day oilbird feeds on have been found in the Green River Formation, suggesting that prehistoric species may have eaten the same fruit and spread the same seeds. Another species from the Upper Eocene has been discovered in France.

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 Guácharo Cave (Oilbird Cave), in the mountainous Caripe district of northern Monagas, Venezuela, 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.

Status and conservation

The Guácharo Cave was Venezuela’s first national monument, and is the centerpiece of a national park; according to some estimates there may be 15,000 or more birds living there. Colombia also has a national park named after its «Cueva de los Guácharos», near the southern border with Ecuador. Oilbirds have been reported in various other places along the Andean mountain chain, including near Ecuador’s Cueva de los Tayos and in Brazil: they are known to dwell as far south as the Carrasco National Park in Bolivia. Dunston Cave, at the Asa Wright Nature Centre in Trinidad, is home to about 200 nesting pairs. Classified as ‘Least Concern’ by the IUCN red list as of October 2016, despite a decreasing population.