Rasolerche
| Rasolerche | ||||||||||||
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Rasolerche ( Alauda razae ) |
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| Scientific name | ||||||||||||
| Alauda razae | ||||||||||||
| ( Alexander , 1898) |
The rasolerche ( Alauda razae ) is a species of bird that is endemic to the uninhabited Cape Verde island of Ilhéu Raso . Because of their tiny distribution area of only 7 square kilometers size it was in 2016 in the endangered Red List species the IUCN as " Critically Endangered (CR) " = "threatened with extinction" classified.
description
The rasolerche is very similar to the closely related skylark , but differs in its stronger, almost chunky and slightly bent beak, the grayer, less reddish-brown tones of plumage and the smaller size. With a length of 12–13 cm, it is only about the size of a goldfinch . The wings and tail are relatively short, which is noticeable , for example, in the hardly existing hand- wing projection. A white trailing edge of the wing is missing. The crown feathers can be set up to form a short hood. Females are significantly smaller and lighter than males. In the male, the average weight is 24 g, the wing length is 87 mm and the beak length is 14.6 mm. Females weigh an average of only 20 g; the hand wing measures 80 mm and the beak 12.2 mm. The beak length of the males in particular varies seasonally, which is probably due to occasional wear and tear when digging.
In adult Rasolerchen the beak is blue-gray with a whitish base of the lower beak. The plumage on the upper side is colored whitish gray with dark streaking. There is a light ring around the eye. The stripe above the eyes is inconspicuously bright. The chin and throat are white, the rest of the underside is yellowish beige with dark pricks on the chest. The control feathers and wings are blackish, the arm covers have bright lace hems. The outer pair of control springs is white. Feet and legs are matt flesh-colored.
In juvenile birds, they are very similar to young skylarks. They also show reddish brown tones, particularly on the ear covers and anterior back. The dotted lines on the chest are more diffuse and the back plumage shows light hems.
voice
The usual call of the Rasolerche is a short trilling chirr-irr-ip . The song is simpler than skylark song and is reminiscent of that of the crested lark . It consists of variations of the call, which are strung in short stanzas with sometimes longer interruptions. It is presented from the ground or in flight. When landing after a singing flight, it is often faster, more complex and then more reminiscent of that of the skylark.
habitat
The Rasolerche is mainly to be found on weathered lava fields below 50 m in height and is particularly tied to dried-up stream beds and sandy areas where sparse vegetation thrives after rainfall. On the south coast of the island, it also inhabits grassy areas on the edge of low cliffs on the coast, and more rarely also depressions closer to the littoral . Outside the breeding season, the majority of the birds can be found in a valley with a gravelly bottom in the east of the island.
nutrition
The rasolerche feeds on plant-based food and insects such as caterpillars or beetles. Occasionally, seeds, sea snails or human food waste are also eaten. It was not clear from the observations whether small skinks are hunted to eat them or to drive them away.
The food is sought on the ground, with the males in particular using their beak to dig in sandy areas. Here especially the tubers are Cyperus Cyperus bulbosus and Cyperus cadamosti dug and dug about 10 cm deep holes for this purpose in about three minutes of work. In some places, the ground has been dug up over a large area. Dominant males also hunt down their recently dug up tubers from others and stubbornly defend their own holes. On gravel-covered ground, food is more likely to be picked up or looked for under small stones. The species can also be found on rocky stretches of coast, where it looks for food or drinks in puddles of seawater. There are no standing fresh water resources on the Ilhéu Raso.
Reproduction
Rasolerche reproduces irregularly whenever enough food is available after rainfall. It usually rains in September and October, after which the breeding occurs between October and December. In principle, however, there can be rain at any time and there are therefore breeding findings from all months. However, if there is no precipitation, the species may not breed for several years.
Rasolerchen lead a monogamous seasonal marriage and during the breeding season the female is closely accompanied by the male. During the singing flight, which usually lasts about two minutes, it rises to a height of about 30 m, shakes and then falls down while singing. Longer singing flights of up to 15 minutes can usually be observed in unpaired males.
The nest is a deep hollow that is lined with grass and is often created under the protection of low yoke leaf plants ( Zygophyllum simplex ). The clutch consists of 1–3 eggs which are only incubated by the female, who is supplied with food by the male. The incubation takes at least 12 days, the nestling duration has not yet been determined. In the event of a brood failure, a new nest is created immediately and a replacement clutch made. The nesting material is recycled.
Breeding success is poor and cases of looted clutches are common. Most likely they go back to the endemic gecko species Tarentola gigas .
Existence and endangerment
The rasolerche is one of the bird species with the smallest brood distribution in the world and is therefore highly threatened. The Ilhéu Raso, which houses the entire breeding population, is only 7 km² in size. Subfossil bone finds suggest that the species also occurred on Santa Luzia , São Vicente and Santo Antão before humans settled Cape Verde in the 15th century , but was then quickly exterminated. There may also have been deposits on the Ilhéu Branco , which was connected to São Vicente, Santa Luzia and Raso during the last Ice Age due to lower sea levels. More recently, the species was only detected outside Raso in 2009 with one specimen near Ponta do Barril on São Nicolau . The individual was almost certainly from Raso.
The population of the rasolerche fluctuates strongly over the years with the weather conditions and can decrease to only about 10 breeding pairs if there is no rain for a long time. If the populations are so low, only a third of the population consists of females.
In the mid-1960s and early 1980s, the occurrence was estimated at 20–50 breeding pairs. However, at the beginning of 1985 150 birds were counted. In 1986 and 1988 the population was counted as 75–100 breeding pairs, after which the results were fairly constant at around 250 individuals. In 1998 and 2003, however, only 92 and 98 birds were found, respectively. After rains in 2004, the population increased to 130 and in 2009 to 190. In November 2011, 1490 birds could be counted.
Against this background, the main threat to the species lies in the advancing desertification of Cape Verde; the global warming could speed this up yet. The high number of clutch losses (presumably by geckos) represents an additional risk and the accidental introduction of rats, cats or dogs could have fatal consequences for the ground-breeding species. The increasing tourism increases this possibility and in 1998 and 2001 traces of cats and dogs were found on Raso. So far, however, there are no indications of a permanent presence or an increase.
The Rasolerche has been protected by law on Cape Verde since 1955 and Raso National Park since 1990. The stock has been recorded regularly since 2001. Educational measures among day-trippers and fishermen are intended to reduce the risk of mammals being introduced to Raso. A possibility of settlement on Santa Luzia is being examined.
literature
- Paul Donald: Raso Lark (Alauda razae) . In: Josep del Hoyo , Andrew Elliott, David Christie: Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona 2014.
Web links
- Alauda razae in the Red List of Threatened Species of the IUCN 2013. Posted by: BirdLife International, 2013. Accessed September 5, 2014.
- xeno-canto: Sound recordings - Raso Lark ( Alauda razae ) , accessed September 5, 2014
- Alauda razae videos, photos, and sound recordings in the Internet Bird Collection , accessed September 5, 2014
Single receipts
- ↑ Alauda razae in the IUCN Red List of Threatened Species 2016.1. Posted by: BirdLife International, 2016. Retrieved October 3, 2017.