Cape Verde Giant Skink

Ilhas Desertas – The terra typica of the Cape Verde giant skink

Organisms that occur in isolated ecosystems such as islands are often adapted to the extreme conditions prevailing there. They exhibit characteristics such as dwarfism or gigantism and often lack defensive mechanisms due to the absence of predators, setting them apart from their mainland relatives. The geographical and ecological isolation of island animals makes them particularly vulnerable to various influences, including hunting, habitat destruction, and introduced predators or food competitors. In historical times, many species affected by island gigantism have become extinct, such as the Rodrigues giant tortoise, the Galápagos giant rat, the St. Helena hoopoe, and the Cape Verde giant skink.

The Cape Verde Islands form the island republic of Cape Verde, located in the Atlantic Ocean. Subfossil finds suggest that the Cape Verde giant skink once inhabited all 15 Cape Verde islands. When the giant skink was discovered in 1784, it was only found on two small, uninhabited islands: Ilhéu Branco, with an area of three square kilometers, and the seven square kilometer Ilhéu Raso (Razo).

The lizard might also have originally been found on the 34-square-kilometer, uninhabited island of Santa Luzia, as indicated by fishermen’s stories. Additionally, the herpetologist José A. Mateo reported finding a lower jawbone of a young Cape Verde giant skink in the feces of a cat on Santa Luzia in 2005. However, a subsequent five-day search for surviving giant skinks on the island was unsuccessful. The Ilhas Desertas, consisting of Branco, Raso, and Santa Luzia, were declared a nature reserve in 1990.

The fact that the Cape Verde giant skink was only found on two or three uninhabited islands at the time of its discovery is no coincidence. With the colonization of Cape Verde by Europeans from 1461, the vegetation on the islands disappeared. Extensive agriculture and the demand for wood led to soil erosion and destroyed the habitat of the skinks (Scincidae). Introduced cats, dogs, rats, green monkeys, cattle, and sheep contributed to the displacement and extinction of the giant skink.

When the British naturalist Charles Darwin visited Cape Verde in 1832, he was already concerned about the lack of biological diversity caused by human intervention.

Cape Verde giant skink – Fact sheet

Alternative name	Bibron’s skink, Cocteau’s skink, Cocteau’s lizard, Lagarto
Scientific name	Chioninia coctei, Macroscincus coctei, Charactodon coctei, Euprepes coctei, Gongylus coctei, Macroscincus coctaei
Original range	Cape Verde Islands (Atlantic Ocean)
Date of extinction	after 1912
Causes of extinction	hunting, habitat loss, introduced animals on islands, drought periods, slow reproduction rate
IUCN status	extinct

Giant lizard with unique features

Due to its heavy body, strong limbs, and long fingers, the Cape Verde giant skink resembles arboreal lizards. Its prehensile tail, which aids in gripping while climbing, also supports this comparison. However, there are no trees or shrubs on Raso and Branco. Instead, these islands have semi-desert conditions. Herpetologist Hans-Hermann Schleich speculates that the Cape Verde giant skink used its “climbing organ” on the rocky cliffs and steep coasts of the islands.

The crepuscular and partially nocturnal Cape Verde giant skink primarily fed on seeds, leaves, and flowers. However, there is also evidence that the lizards preyed on bird eggs and fledglings. Schleich mentions that the Cape Verde giant skink lived commensally with seabirds in rock crevices on the islands and is said to have fed on dead birds.

One unique feature of the Cape Verde giant skink was its freely movable eyelids. The lower eyelid had a transparent window, allowing the skink to see approaching predators or other threats from below even when its eyes were closed.

Interestingly, while eggs of the Cape Verde giant skinks can be found in various museums, indicating that they were oviparous (egg-laying), scientists also discovered belly button slits on preserved specimens, suggesting they were viviparous (live-bearing). In his 2004 biometric analysis of the extinct giant skink, Brian Lee Schnirel points out that some skinks can switch from viviparous to oviparous and vice versa. This might have also been the case for the Cape Verde giant skink.

Cape Verde giant skink: Food source, fat salve provider, and shoe material

As with many other island species, a combination of natural and anthropogenic factors caused the extinction of the Cape Verde giant skink. These factors certainly include active hunting, introduced predators and food competitors, as well as the occurrence of exceptional drought periods.

Schleich emphasizes human intervention over natural climatic changes when discussing the disappearance of this reptile species. He highlights the devastating impact of the release of convicts on the island of Branco in 1833. The half-starved men ate the Cape Verde giant skinks living there, which massively affected the population numbers. Even later, people resorted to the lizard as a food source during drought periods.

Additionally, the lizards lived together with seabirds in rock crevices, making them “bycatch” during bird-catching activities. Schleich also reports on fishermen who used bamboo or reed sticks with attached fishing hooks to pull young, nest-dwelling Cape Verde shearwaters (Calonectris edwardsii) from their nests under the rock crevices. Not infrequently, they also caught giant skinks, which they sold to doctors and pharmacists. These professionals used the fatty meat of the lizards to make traditional pain salves, such as those used to treat joint diseases. Records (1873) by the Portuguese zoologist J. V. Barbosa du Bocage also show that the giant lizards were hunted for their skins to make shoes.

Even today, fishermen in Cape Verde practice bird-catching. It is estimated that annually 5,000 young birds are pulled from nests on Raso and Branco. Consequently, the population numbers of the Cape Verde shearwater are also declining. The IUCN currently lists the bird species as ‘near threatened’.

Additional reasons for the disappearance of the giant skink

On Santa Luzia, invasive animals introduced by humans caused the disappearance of the giant skinks. Cats, dogs, and rats are considered the predators that posed the greatest threat to the lizards. The IUCN also points out that predatory rats and cats in seabird colonies competed with the lizards for food.

A slow growth and reproduction rate of the lizards may have also contributed to the declining population numbers. In 2003, biologists Franco Andreone and Fabio M. Guarino conducted a study on the age structure of the giant lizards. Based on skeletochronological analyses, the scientists estimated a minimum life expectancy of 16 years for male giant skinks and 12 years for females. Males likely reached sexual maturity at five years of age and females at six years.

Museum collections contain almost exclusively adult Cape Verde giant skinks. Andreone and Guarino could only locate two juveniles. It is unclear whether collectors at the time preferred adult specimens or if the giant skink populations predominantly consisted of adult animals.

Additionally, expedition travelers, collectors, and traders have always been interested in the Cape Verde giant skink – likely due to its peculiar morphology and size. When Jose Dasilva Fejo discovered the giant skink in 1784, he took several specimens with him to Lisbon. Nearly a hundred years later, Bocage arranged for three live skinks to be brought to Lisbon. Two died shortly after their arrival, with one surviving for four years. The Italian herpetologist Mario Giacinto Peracca brought more than 40 animals to Italy in 1891, all of which died.

Especially in the 19th and early 20th centuries, traders sold the reptiles to naturalists and natural history museums. As a result, numerous museums housed specimens of Cape Verde giant skinks and their eggs at the turn of the century. Various European zoos also acquired giant skinks in the early 20th century; however, the animals never reproduced in captivity.

Cape Verde giant skink – When exactly it disappeared remains uncertain

The Italian zoologist Leonardo Fea traveled to the Cape Verde Islands in 1898 and was likely one of the last scientists to see living Cape Verde giant skinks in their natural habitat. Fea also brought back many specimens of the “fantastic giant skink” along with some “rare birds” from his expedition to Italy, despite being aware that there were only a few individuals of this species left.

Scientists date the extinction of the Cape Verde giant skink to a period between 1914 and 1940. According to the IUCN, the last live sighting of the Cape Verde giant skink was in 1912. However, the most recent evidence of a young giant skink dates to 2005, from cat feces on the island of Santa Luzia. Were there still specimens of the Cape Verde giant skink on Santa Luzia until 2005? Searches for surviving Cape Verde giant skinks on Santa Luzia were unsuccessful. There is little hope since the cat population has increased since 2005, and the invasive animals are now found all over the island.

Schleich had already searched for the Cape Verde giant skink on the islands of Branco, Raso, and Santa Luzia in 1979. In his report, Letzte Nachforschungen zum kapverdischen Riesenskink, Macroscincus coctei (1982), he summarized the result of his search as follows:

“After intensive research and questioning of the Cape Verde population (mostly fishermen) and the results of three of my own research trips to the Terra typica of the giant skink at various times of the year, there is no longer any hope for the survival of the species.”

Letzte Nachforschungen zum kapverdischen Riesenskink, Macroscincus coctei (DUMERIL & BIBRON 1839) (Reptilia: Sauria: Scincidae). Salamandra 18, 1982. pp. 10-12. H.-H. Schleich.

The IUCN officially listed the Cape Verde giant skink as extinct in 2013, after the reptile had not been sighted for a hundred years despite numerous search expeditions.