Fettschwalm

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Fettschwalm
Two fat swallows in Trinidad

Two fat swallows in Trinidad

Systematics
Class : Birds (aves)
Order : Swallow-like (Caprimulgiformes)
Family : Fat swallows (Steatornithidae)
Genre : Fat swallows
Type : Fettschwalm
Scientific name of the  genus
Steatornis
Humboldt , 1814
Scientific name of the  species
Steatornis caripensis
Humboldt , 1817
Steatornis caripensis

The fat swallow ( Steatornis caripensis ) or Guácharo is the only recent species of the bird family of the fat swallow (Steatornithidae). The monotypical classification in a separate family is due to the fact that the Fettschwalm is very unusual.

Most fat swallows nest in caves or between rocks, less often in trees. They are the only flightable, nocturnal birds that feed on fruits (the kakapo is flightless). They have a specially adapted sense of sight and are one of the few species of birds that can orientate themselves like bats through echolocation .

The species is included in the order of the swallow-like (Caprimulgiformes) and there is a relationship to the nightjar , but recent osteological comparisons also suggest a closer relationship to the trogons (Trogoniformes).

anatomy

The Fettschwalm is a reddish-brown bird about 40 to 49 centimeters tall with white spots on its throat, head and wings. It weighs between 350 and 375 grams. The plumage of males and females is the same. Its large beak opening is used to transport food to the nesting site.

It also has relatively long wings and a long tail. The feet are small and are particularly suitable for clinging to vertical surfaces.

Fat swallows have a very good sense of smell.

The eyes are adapted to the nighttime foraging. They are rather small, but have a large pupil , which means they have the highest light sensitivity of all bird species (the f-number is 1.07).

The retina is dominated by the rod cells. With 1,000,000 rods per mm 2 , their density is higher than that of any other vertebrate animal. The rods are arranged in layers, which otherwise only occurs in deep-sea fish , but not in birds. The number of cone cells is low. Due to this special characteristic, the eyes of the fat swallows may be significantly worse in daylight than at night.

distribution

The Fettschwalm occurs in northern and central South America , from eastern Panama via Colombia and Venezuela to the east to Trinidad and Guyana and along the Andes to the south via Ecuador and Peru to central Bolivia .

Way of life

The fat swallow is the only nocturnal, fruit-eating bird in the world. During the day he stays in colonies in up to a kilometer long, completely dark burrows in the ground, in which he can no longer see anything despite his night eyes.

In these dark caves, which serve as resting and nesting places, but not outside, he orients himself by means of echolocation , which is similar to that of bats . The click signals generated in this way have a low frequency (1.5–2.5 kHz ) and are therefore, unlike those of bats, audible to humans. In the group, fat swallows produce a deafening noise level, so that the fat swallow is considered the "loudest of all birds".

At night, it covers up to 75 kilometers in search of food. Its diet consists, among other things, of the oily fruits of palm trees and bay leaves . It grabs the fruit with its strong beak and swallows it whole. The next day the food is digested in its resting place.

Fat swallows live in colonies that can grow up to 50 pairs in size. The nest is a mound of dried mud, droppings and strangled fruits.

Reproduction

The female usually lays two to four eggs, which are hatched by the two parents together. The young hatch after a breeding period of about 23 days. In their first weeks of life, they are fed on palm fruits and so build up large fat reserves until they have twice the weight of their parents.

The scientific discovery

Alexander von Humboldt described the species during his South America expedition in Venezuela in the cave " Cueva del Guácharo " in the national park of the same name, which is located in the state of Monagas about 13 kilometers from Caripe . The cave is named after the fat swallow, which is called Guácharo there. Humboldt and his friend, the young doctor and botanist Aimé Bonpland , explored the front section of this 10.5 km long stalactite cave in South America on September 18, 1799 and shot two specimens. He reports that the inhabitants collect the young birds shortly before they fled and obtain oil from them by boiling them for hours, hence the English name "Oilbird".

Humboldt noted:
“The Guacharo is the size of our chickens, the throat of goat milkers and Procnias, the shape of vulture-like birds with tufts of stiff silk around their crooked bills. (...) Its plumage is dark gray-blue, with small black stripes and spots; The head, wings and tail show large, white, heart-shaped, black-lined spots. The bird's eyes cannot stand the daylight, they are blue and smaller than those of the goat milkers. (...) It is difficult to get an idea of ​​the noise that thousands of birds make in the dark interior of the cave (...) Only after several fruitless attempts did Bonpland manage to shoot two Guacharos, which, blinded by the torchlight, fluttered after us . This gave me the opportunity to draw the bird, which until then had been completely unknown to naturalists. "

swell

Individual evidence

  1. ^ A b G. Martin, LM Rojas, Y. Ramírez, R. McNeil: The eyes of oilbirds ( Steatornis caripensis ): pushing at the limits of sensitivity . In: Natural Sciences . tape 91 , no. 1 , 2004, p. 26-29 , doi : 10.1007 / s00114-003-0495-3 .
  2. ↑ LM Rojas, Y. Ramírez, R. McNeil, M. Mitchell, G. Marín: Retinal Morphology and Electrophysiology of Two Caprimulgiformes Birds: The Cave-Living and Nocturnal Oilbird ( Steatornis caripensis ), and the Crepuscularly and Nocturnally Foraging Common Pauraque ( Nyctidromus albicollis ) . In: Brain, Behavior and Evolution . tape 64 , no. 1 , 2004, p. 19-33 , doi : 10.1159 / 000077540 ( karger.com ).
  3. ↑ Fettschwalm  (Steatornis caripensis)  in the Encyclopedia of Life . Retrieved August 12, 2017.
  4. ↑ National Geographic

literature

Web links

Commons : Steatornis caripensis  - collection of images, videos and audio files