Raso lark

Last updated

Raso lark
Razo lark.jpg
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Alaudidae
Genus: Alauda
Species:
A. razae
Binomial name
Alauda razae
(Alexander, 1898)
Raso lark range.png
Synonyms
  • Calandrella razae
  • Spizocorys razae

The Raso lark (Alauda razae) is a small passerine bird with a highly restricted range, being found only on Raso islet in the Cape Verde Islands. This critically endangered member of the family Alaudidae lives in very arid terrain, and is considered one of the least known birds in the Western Palaearctic region, due to its remoteness and the lack of much ornithological study on the archipelago as a whole.

Contents

Taxonomy and systematics

Originally, the Raso lark was classified as belonging to the genus Spizocorys . Formerly or presently, some authorities considered the Raso lark to belong to the genus Calandrella . [2] Alternate names for the Raso lark include Cape Verde Islands lark, Raso Island lark, Raso short-toed lark and Razo skylark.

Description

SpizocorysRazaeKeulemans.jpg

Raso larks are relatively small in size. The Raso larks can range from sizes between 14 and 18 cm. The adult population is mostly made up of males who are larger than the females. The body has black and brown short streaks and paler around the chest with an erectile crest. The bill is thick-based and robust, longer for the males. The Raso lark is considered an adult when it has developed a reddish-brown tone between the ears and tail, with a pattern on the crown and back. While in flight they display a short tail with short broad wings. The tail and edge of the wings are white.

Distribution and habitat

The Raso lark is restricted in range to only Raso islet in the Cape Verde archipelago, although historically it is believed to have ranged over two other islands, Branco and São Vicente Island. All three of these islands were joined in the last ice age. Evidence from subfossil bone deposits reveal that the Raso lark once also existed on the islands of Santa Luzia, São Vicente, Santo Antão, and possibly Branco during the glacial times, before human colonization in the 15th century. Unfortunately, colonization was followed by a rapid extinction of local fauna. Raso islet itself has no permanent water and has never been inhabited by people, a fact that has probably saved the lark from extinction until now.

The island consists mostly of rocky desert with sandy parts in the west. Most Raso larks are found on level plains with volcanic soil and are associated with small vegetated patches along dry stream beds in which it feeds and breeds. Suitable breeding grounds on the island of Raso cover less than half of the island. The barren island suffers from frequent droughts which create dry plains that force the Raso larks to move across the island in search for food. Their most common areas of habitation are near dry river beds, but due to the scarcity of water, only patches of vegetation remain for Raso larks to reside in. Their nesting and feeding grounds consist of those same areas where vegetation is available. The Raso lark's sensitivity to drought has kept it endangered for several years due to the dry climate on the Cape Verde islands.

Behaviour and ecology

A number of desert-dwelling larks have evolved long bills to aid in digging for food in the sandy environment but the enlarged bill of the Raso lark has evolved for dominance displays among males. [3] Flocks have also been observed feeding among rocks close to the sea, and the birds excavate holes in sandy soil to extract the small bulbs of nutsedges, which are perennial weeds in the sedge family that superficially resemble grasses.

Breeding

Breeding is very unpredictable, as it is dependent on the occurrence of rain. Courtship behaviour is similar to that of the Eurasian skylark. The male courts the female by singing softly, raising its chest, and hopping up and down while the wings are spread open. Once done mating, both the male and female collect dried grass in order to build a nest. The male defends the nesting site while the female finds a safe location to build a nest.

The female Raso lark lays one to three eggs per clutch, usually a day apart. The incubation time is thought to be 15 days. During incubation the female sits on the eggs for ten-minute intervals and then goes off to find food. The Raso lark population changes rapidly in response to rain, and has fallen to extremely low levels during droughts (Ratcliffe et al. 1999, Donald et al. 2003, Donald and Brooke 2006). The females, even though smaller in size, still provide by gathering bulbs while the males stay in the burrows and vigorously watch over the nest, protecting it from outside intruders. The Raso lark is not considered very fit for reproductive success and their reproductive success is very low. The adult sex ratio is unbalanced, with a high proportion of the population being male.

Food and feeding

The Raso lark feeds by digging in the ground for insect larvae, and bulbs of the nutsedge. Both sexes also feed on grass seeds, and insects such as butterflies, moths and grasshoppers. Food and water for the Raso lark is scarce during the drought seasons. These necessities are provided by eating Cyperus bulbosus or Cyperus cadamosti which are bulbs of nutsedges. Males and females have different-sized bills, which is why it was thought that males fed more on bulbs than females do. To get to a bulb the Raso lark must use its beak to dig burrows in the sandy soil. New studies are showing that males consume more bulbs than females not because of the difference in bill size; males' bills are 20% larger than females' bills (Donald 2007); but males consume more bulbs because males control the territories (Donald 2007). Females can dig the burrows just as well as the males. Males dig 0.32 bulbs per minute and females dig 0.36 bulbs per minute (Donald 2007). Males dig for 61.8 seconds while females dig for 58.0 seconds (Donald 2007). Females are just as adequate at digging as males, but they only spend about 1/3 as much time digging as males do. Because of this, females spend significantly more time feeding from the surface (Donald 2007). The males protect these territories, which usually have more than one burrow that provides them with food, even from the females of their species (Donald 2007). Females are dying at a much faster rate because of this and because their only source of food without the bulbs are insects and grass seeds. Females spend a larger portion of their time foraging which means less time looking out for predators and they also have a higher food stress which both can lead to their deaths (Donald 2007). During times of little food, the females are the ones to die from starvation because they have to find bulbs for the male and incubate the eggs.

Threats

The Raso lark is threatened by predators such as the Cape Verde giant gecko and birds such as the lesser Cape Verde kestrel, brown-necked raven, and Cape Verde barn owl, which make it difficult for them to survive. Additionally, Raso larks are vulnerable to the threat of accidental introduction of cats, dogs, rats by fishermen or other visitors to the island. Within the habitat of the Raso lark, the Cape Verde giant geckos weigh roughly 100 g and include juvenile birds in their diet. The Cape Verde Giant Gecko eats most chicks and eggs before they are hatched and fledged. Many aspects of the species’ ecology and behaviour closely resemble that of the Eurasian skylark.

Status

The tiny population size, which fluctuates from ~200-1,000 birds, coupled with the highly skewed sex ratio (around two males to each female) make this species critically endangered. The reproductive success of the birds is very low, likely due to predation by the near-endemic Cape Verde giant gecko. Although the island is currently free of mammalian predators such as rats or feral cats, and is a closed reserve, the likelihood of a single accidental introduction causing catastrophic damage remains high. It has been proposed that re-establishing a second population on the gecko-free island of Santa Luzia should be a conservation priority.

Related Research Articles

<span class="mw-page-title-main">Lark</span> Family of birds

Larks are passerine birds of the family Alaudidae. Larks have a cosmopolitan distribution with the largest number of species occurring in Africa. Only a single species, the horned lark, occurs in North America, and only Horsfield's bush lark occurs in Australia. Habitats vary widely, but many species live in dry regions. When the word "lark" is used without specification, it often refers to the Eurasian skylark (Alauda arvensis).

<span class="mw-page-title-main">Procellariidae</span> Family of seabirds which includes petrels, shearweters and prions

The family Procellariidae is a group of seabirds that comprises the fulmarine petrels, the gadfly petrels, the diving petrels, the prions, and the shearwaters. This family is part of the bird order Procellariiformes, which also includes the albatrosses and the storm petrels. Whilst agile swimmers and excellent in water, petrels have weak legs and can only shuffle on land, with the giant petrels of the genus Macronectes being the only two species that can properly walk.

<span class="mw-page-title-main">Eurasian skylark</span> Species of bird

The Eurasian skylark is a passerine bird in the lark family, Alaudidae. It is a widespread species found across Europe and the Palearctic with introduced populations in New Zealand, Australia and on the Hawaiian Islands. It is a bird of open farmland and heath, known for the song of the male, which is delivered in hovering flight from heights of 50 to 100 metres. The sexes are alike. It is streaked greyish-brown above and on the breast and has a buff-white belly.

<span class="mw-page-title-main">Burrowing owl</span> Species of owl

The burrowing owl, also called the shoco, is a small, long-legged owl found throughout open landscapes of North and South America. Burrowing owls can be found in grasslands, rangelands, agricultural areas, deserts, or any other open, dry area with low vegetation. They nest and roost in burrows, such as those excavated by prairie dogs. Unlike most owls, burrowing owls are often active during the day, although they tend to avoid the midday heat. Like many other kinds of owls, though, burrowing owls do most of their hunting during dusk and dawn, when they can use their night vision and hearing to their advantage. Living in open grasslands as opposed to forests, the burrowing owl has developed longer legs that enable it to sprint, as well as fly, when hunting.

<span class="mw-page-title-main">Zino's petrel</span> Small seabird in the gadfly petrel genus

Zino's petrel or the freira, is a species of small seabird in the gadfly petrel genus, endemic to the island of Madeira. This long-winged petrel has a grey back and wings, with a dark "W" marking across the wings, and a grey upper tail. The undersides of the wings are blackish apart from a triangle of white at the front edge near the body, and the belly is white with grey flanks. It is very similar in appearance to the slightly larger Fea's petrel, and separating these two Macaronesian species at sea is very challenging. It was formerly considered to be a subspecies of the soft-plumaged petrel, P. mollis, but they are not closely related, and Zino's was raised to the status of a species because of differences in morphology, calls, breeding behaviour and mitochondrial DNA. It is Europe's most endangered seabird, with breeding areas restricted to a few ledges high in the central mountains of Madeira.

<span class="mw-page-title-main">Black lark</span> Species of bird

The black lark is a species of lark in the family Alaudidae found in south-eastern Russia and Kazakhstan.

<span class="mw-page-title-main">Crested lark</span> Species of bird

The crested lark is a species of lark widespread across Eurasia and northern Africa. It is a non-migratory bird, but can occasionally be found as a vagrant in Great Britain.

<span class="mw-page-title-main">Malabar lark</span> Species of bird

The Malabar lark, or Malabar crested lark is a species of lark in the family Alaudidae found in western India.

<span class="mw-page-title-main">Cape Verde shearwater</span> Species of bird

The Cape Verde shearwater, or cagarra locally, is a medium-large shearwater, a seabird in the petrel family Procellariidae. It is endemic to the Cape Verde archipelago of Macaronesia in the Atlantic Ocean, off the coast of West Africa.

<span class="mw-page-title-main">Greater hoopoe-lark</span> Species of bird

The greater hoopoe-lark is a passerine bird which is a breeding resident of arid, desert and semi-desert regions from the Cape Verde Islands across much of northern Africa, through the Arabian peninsula, Syria, Afghanistan, Pakistan and India. It was formerly known as the bifasciated lark and sometimes as the large desert lark.

<span class="mw-page-title-main">Ilhéu Raso</span> Island of Cape Verde

Ilhéu Raso is an uninhabited 5.76 square kilometres volcanic island in the Barlavento archipelago of Cape Verde. It is flanked by the smaller Branco islet to the west and by São Nicolau island on its eastern side, distance is 15 kilometres from the island of São Nicolau. Together with Santa Luzia and Ilhéu Branco, Ilhéu Raso is on the tentative list of UNESCO's World Heritage Sites. Since 1990, the islet is part of the protected area Reserva Natural Integral de Santa Luzia.

<span class="mw-page-title-main">Ilhéu Branco</span> Island of Cape Verde

Ilhéu Branco is an uninhabited 278-hectare (690-acre) islet in the Barlavento group of the Cape Verde archipelago off the coast of north-west Africa in the Atlantic Ocean. Ilhéu Branco is flanked by the islands of Santa Luzia to the north-west and Ilhéu Raso to the south-east. Since 1990, the islet is part of the protected area Reserva Natural Integral de Santa Luzia. Together with Santa Luzia and Ilhéu Raso, Ilhéu Branco is on the tentative list of UNESCO's World Heritage Sites.

<span class="mw-page-title-main">Cape Verde Islands dry forests</span> Ecoregion off West Africa

The Cape Verde Islands dry forests is a tropical and subtropical dry broadleaf forests ecoregion in the Cape Verde Islands, which constitute the country of Cabo Verde. The islands lie off the western coast of Africa.

<i>Alauda</i> Genus of birds

Alauda is a genus of larks found across much of Europe, Asia and in the mountains of north Africa, and one of the species endemic to the islet of Raso in the Cape Verde Islands. Further, at least two additional species are known from the fossil record. The current genus name is from Latin alauda, "lark". Pliny the Elder thought the word was originally of Celtic origin.

<span class="mw-page-title-main">Iago sparrow</span> Species of bird

The Iago sparrow, also known as the Cape Verde or rufous-backed sparrow, is a passerine bird of the sparrow family Passeridae. It is endemic to the Cape Verde archipelago, in the eastern Atlantic Ocean near western Africa. Females and young birds have brown plumage with black marks above, and a dull grey underside, and are distinguished from other species of sparrow by their large, distinct supercilium. Males have a brighter underside and bold black and chestnut stripes on their head. At 12.5–13 centimetres (4.9–5.1 in) long, it is a smaller sparrow. This bird's vocalisations are mostly variations on its chirp, which differ somewhat between males and females.

<i>Gopherus</i> Genus of tortoises

Gopherus is a genus of fossorial tortoises commonly referred to as gopher tortoises. The gopher tortoise is grouped with land tortoises that originated 60 million years ago, in North America. A genetic study has shown that their closest relatives are in the Asian genus Manouria. The gopher tortoises live in the southern United States from California's Mojave Desert across to Florida, and in parts of northern Mexico. Gopher tortoises are so named because of some species' habit of digging large, deep burrows. Most notably, Gopherus polyphemus digs burrows which can be up to 40 feet (12 m) in length and 10 feet (3.0 m) in depth. These burrows are used by a variety of other species, including mammals, other reptiles, amphibians, and birds. Gopher tortoises are 20–50 cm (7.9–19.7 in) in length, depending on the species. All six species are found in xeric habitats. Numerous extinct species are known, the oldest dating to the Priabonian stage of the Late Eocene of the United States.

<i>Cyperus bulbosus</i> Species of plant

Cyperus bulbosus is a species of sedge found across Africa, the Middle East, Indian subcontinent, Southeast Asia, and Australia. In Australia, it is commonly called Nalgoo or (Australian) bush onion or "wild onion", but is not related to the onion or other Alliaceae. It is a component of Australian bushfood, but is considered an agricultural weed in other areas.

<span class="mw-page-title-main">Wildlife of Cape Verde</span> Endemic species of the West African island nation

The wildlife of Cape Verde is spread over its archipelago of ten islands and three islets, which all have parks under their jurisdiction by decree promulgated by the Cape Verde government. Located off the west coast of Africa, the total land area of the island nation is 4,564 square kilometres (1,762 sq mi). The wildlife consists of many tropical dry forest and shrub land, endemic flora and fauna, and rare breeding seabirds and plants, which are unique to this group of islands.

<span class="mw-page-title-main">Black-crowned sparrow-lark</span> Species of bird

The black-crowned sparrow-lark is a species of lark in the family Alaudidae. It is found across northern Africa from Mauritania through the Middle East to north-western India. Its natural habitat is dry savanna.

<span class="mw-page-title-main">Magnificent frigatebird</span> Species of bird

The magnificent frigatebird is a seabird of the frigatebird family Fregatidae. With a length of 89–114 centimetres and wingspan of 2.17–2.44 m it is the largest species of frigatebird. It occurs over tropical and subtropical waters off America, between northern Mexico and Perú on the Pacific coast and between Florida and southern Brazil along the Atlantic coast. There are also populations on the Galápagos Islands in the Pacific and the Cape Verde islands in the Atlantic.

References

  1. BirdLife International (2018). "Alauda razae". IUCN Red List of Threatened Species . 2018: e.T22717428A131103086. doi: 10.2305/IUCN.UK.2018-2.RLTS.T22717428A131103086.en . Retrieved 19 November 2021.
  2. "Alauda razae - Avibase". avibase.bsc-eoc.org. Retrieved 2016-12-05.
  3. Kingdon, Jonathan (1989). Island Africa: The Evolution of Africa's Rare Plants and Animals. Princeton, New Jersey: Princeton University Press. p.  39. ISBN   0-691-08560-9.