Bioko drill

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Mainland drills, from Cameroon. They bear a strong resemblance to the Bioko drill, as they are part of the same species, Mandrillus leucophaeus; however, the Bioko drill is distinguished by a yellow crown, rather than white. Drills (Mandrillus leucophaeus) captive specimens ... (21571062871).jpg
Mainland drills, from Cameroon. They bear a strong resemblance to the Bioko drill, as they are part of the same species, Mandrillus leucophaeus; however, the Bioko drill is distinguished by a yellow crown, rather than white.

Bioko drill [2]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Infraorder: Simiiformes
Family: Cercopithecidae
Genus: Mandrillus
Species:
Subspecies:
M. l. poensis
Trinomial name
Mandrillus leucophaeus poensis
Zukowsky, 1922

The Bioko drill (Mandrillus leucophaeus poensis) is a subspecies of the drill, an Old World monkey. It is endemic to Bioko Island, Equatorial Guinea, [4] located off the west coast of Africa. [5] The drill is one of the largest monkey species, and is considered endangered. [5] The Bioko drill was separated from their mainland counterpart, due to rising sea levels after the end of the last ice age, around 10,000 years ago. [4]   The capital of Equatorial Guinea, Malabo, [4] is on Bioko Island. The Malabo market is the primary point of sale for bushmeat on Bioko Island. [1] The drill plays an important role in the cultural tradition of bushmeat consumption, and is locally considered to be tasty, and in some regions, a delicacy. [6] The commercialisation of hunting on Bioko Island has made this practice unsustainable. [1] Hunting of the Bioko drill is banned in most areas of Bioko Island, as they predominantly inhabit protected areas on the island. However, the ban is considered ineffective; hunting remains the largest threat to the drill's population. [4] [7]

Contents

Description

The Bioko drill is of a similar appearance to the mainland drill, with a green-brown coat and white fur on the underbelly. [5] It is distinguished by a yellowish crown of fur with black tips that lines the drill’s face, while the mainland drills have a crown that is mostly white. [5] The drills are also extremely sexually dimorphic with the males being much larger, weighing 20 kg on average in adulthood, whereas females typically reach 8.5 kg. [7] However the length of a fully grown adult, excluding the tail, is quite similar between the sexes, with males reaching an average of 67 cm and females averaging 54 cm. [7] The males have a shiny black face with sharp features, and an elongated muzzle. [8] They are further distinguished by purple, blue and red hair on their rump and a white fur on their chin. [8]

Behaviour

Social behaviour

In lowland areas, Bioko drills are known to commune in areas that are known to have consistent food sources to eat together, returning to favoured spots. [9] They are highly social animals that live in groups of around 20, or even up to 30 individuals, [6] predominantly made up of adult and adolescent females. [8] They are also highly vocal and are easy to track through their callings. [10] [6] The Bioko drill will also respond to distress bleats from duikers. [6] While they spend most of their time on the forest floor during the day, they tend to sleep in trees. [8]

Foraging behaviour

The Bioko drill is a primarily terrestrial monkey, and will forage in groups for several hours a day on the forest floor, [10] though they will quickly climb trees when threatened by hunting dogs. [6] They have also been observed to engage in intelligent feeding behaviours, such as breaking millipedes in half to suck out the innards, stripping stems in order to consume the innermost pith, and searching pith for larvae. [10] The Bioko drill is also known as a primary seed disperser, contributing to tree dispersal through their consumption of tree seeds and fruits. [9] Their effectiveness is due to their terrestrial nature, as they consume more dropped, and therefore more mature fruits, the seeds of which are dispersed with their faecal matter. [11] The hunting of the Bioko drill has been correlated with a loss of hardwood trees and sapling undergrowth. [9] Recent observations have seen the drills move from preferentially eating fruits to consuming more herbaceous material due to hunting pressures. [9] This has led the drills to forage for an increasingly long period and they now forage for a longer time than any other primate on the island. [9]

Ecology

A map of Bioko Island, which holds the endemic subspecies, the Bioko drill. The drill lives primarily in southern parts of the island due to denser rainforest alleviating hunting pressures, however infrastructural advances threaten this. Bioko.png
A map of Bioko Island, which holds the endemic subspecies, the Bioko drill. The drill lives primarily in southern parts of the island due to denser rainforest alleviating hunting pressures, however infrastructural advances threaten this.

Range and habitat

The biomes on Bioko Island are typically categorised into three subtypes; tropical rainforests in the lower regions, montane forest, which is typified by higher humidity, a lower temperature, and is dominated by tree ferns, and mossy forests at highest altitudes. [12] While the Bioko drill will preferentially inhabit lowland forests, tending to larger groups in these areas, [9] populations have been found inhabiting areas up to 2,000m above sea level in grasslands and areas with dense undergrowth. [10] Lowland populations tend to be more diverse, potentially due to a higher diversity of vegetation, [9] with fruits more prevalent at lower altitudes and higher altitudes more conducive to more fibrous sources of food such as herbs and ferns. [10]

There are also comparatively higher densities in populous reached to the south and east of the island, due to a relative lack of road infrastructure, and hunting out of drills in the northern parts of Bioko. [4] The inaccessibility of these regions for hunters allows the drills to reach greater populations without hunting pressure. [4] [1] However, there is rapid road and infrastructure development that may put these populations at further risk. [1] One such road runs through the Gran Caldera Southern Highlands Reserve, a protected area in the south of Bioko Island, where the drill's population is most dense. [1] This also poses an issue to habitat range of the Bioko drill as their population density is lowest around roads. [4]

Diet

The diet of the Bioko drill is largely dependent on their location on the island, with lowland drills primarily consuming a frugivorous diet, similar to the mainland drill, whereas drills living in more mountainous areas preferably feed on herbaceous materials such as pith, leaves and fungi, though these are significantly less nutritious. [10] [9] Those higher altitude drills consume a greater range of components, including the pith, stalk, flowers, seeds, leaves, and roots of a plant, rather than just the fruits. [10] They are also capable of husking coconuts to consume them. [6] The drill diet may also consist of wood and mushrooms, the latter of which is rare in a primate. [10] Bioko drills are also known to consume animals, including most commonly; beetles, land crabs and other crustaceans, millipedes and hymenopterans, a class that includes ants, flies, wasps, [10] and the African giant snail. [6] In one instance, the remains of rodents and frogs were found in faecal matter of a drill, [10] and they have also been noted to forage for marine turtle eggs on beaches. [6] Additionally, the drill's response to distress calls of duikers may be indicative of their willingness to consume them. [6]

Conservation status

Threats from hunting

The Bioko drill is considered endangered, and is highly threatened by the bushmeat trade. [7] Primates such as the drill that have larger bodies, are slower growing, and are mainly terrestrial, are considered to be disproportionately affected by hunting, and as of 2009, it was predicted that the drill population on Bioko Island was around 4,000. [9] [7] The mean biomass of Bioko’s forests are being depleted, with larger mammals preferentially hunted, [4] and Bioko drills being intolerant to hunting. [13]

The bushmeat trade has increasingly posed a threat to wildlife on Bioko Island as hunters have switched from using trappings to shotguns. [1] This increases carcass volume available to hunters, as well as allowing hunters to selectively target animals that will fetch a greater price. [1] Being the largest primate on Bioko Island, the drill is also one of the most expensive and therefore sought after by hunters. [7] Bioko drills are more easily hunted with the assistance of dogs and shotguns, and hunters will sometimes mimic the bleat of a duiker to find them. [6]

Regulation of bushmeat hunting has had little effect, as announcements of imminent hunting bans are predictive of surges in carcass levels seen at the bushmeat market, thought to be a result of panic and an increased economic incentives, and bans themselves remaining unenforced. [1] Several laws have been implemented to this effect. A law came into place in 2003, prohibiting hunting in certain areas, and in 2007 there was a law announced that would prohibit the hunting, selling and consumption of bushmeat. [1] The law was announced in October and implemented in November. After the laws announcement, but before its implementation, the market for bushmeat became much larger and grew increasingly profit-orientated, as indicated by a rapid increase in carcasses available on the bushmeat market. At the date of the law's implementation, carcass rates had nearly disappeared, however they rapidly increased from that point due to a lack of enforcement. The market had completely rebounded by 2008, eventually reaching higher levels than before the law was announced and peaking in April, 2010 at 37 carcasses per day. [1] These hunting practices remain financially lucrative, as the price of the Bioko drill continues to increase. [4]

Other threats

While drills are not often observed in or near agricultural areas, they can be considered pests, and shot by farmers to protect crops, [9] [6] particularly by the Bubi, the native people of Bioko, who tend to be predominantly agricultural, and live closer to greater populations of the drill. [6]

Loss of habitat due to climate change will primarily affect lowland areas in Bioko Island, due to rising sea levels disturbing those regions. This will likely affect large proportions of the drill’s population, [10] as the lowland habitats are conducive to larger groups of drills, and are generally preferred. [10]

There is some evidence that Bioko drills captured from the wild may used in circuses. [14] This poses a threat to drills as in captivity they express long term signs of stress and may act aggressively, decreasing their ability to mate [14] if they are rescued. This also removes them from their natural habitat and population, removing them from gene pools that are already depleted by hunting.

Interaction with humans

Bushmeat culture

Bioko Island contains a large bushmeat market, the Malabo market, [4] which is quite similar to those of mainland Africa. [4] Bushmeat itself is an important resource for Bioko Island, both economically and nutritionally, [9] and both hunting and consumption have increased in relation to Equatorial Guinea's GDP. [1] Bushmeat is preferably consumed over other sources of protein by the island's two major ethnic groups, the Bubi and the Fang, though the Fang show a higher preference for primates specifically. [13]

Commercialisation and modernisation of hunting practices has led to a focus on shotgun use over trappings, as these methods are more lucrative. [1] Additionally, growing infrastructure on Bioko Island has allowed a faster return rate for hunters and intermediaries for the market, who are often taxi drivers, allowing for faster travel and reward. [1] The Bioko drill is a popular target amongst bushmeat hunters, [7] and increased prices of the drill as its population declines has been speculated to encourage hunters to seek it out in increasingly remote areas, furthering its decline. [4] The Bioko drill tends to be sold freshly killed, and rarely smoked or live. [1] While bushmeat hunted in Bioko is predominantly sold in the Malabo market, or elsewhere on the island itself, the majority of bushmeat hunters are from mainland Equatorial Guinea. [13] Consumption of bushmeat in Bioko has increasingly become indicative of wealth and status, as the price of the meat rises, [1] however it still remains a commonly accessed source of protein. [15]

There has been some concern that the proximity of the drill to humans due to deforestation, hunting, and consumption could result in zoonotic disease transmission. [15] [1]

The Bioko drill has been suggested to be an important link in the study of Simian immunodeficiency virus [16] (SIV) due to its long history of isolation from the mainland. Independent evolution of the disease in the Bioko drill for 10,000 years has allowed comparison with the mainland drills, and offers an observation into macroevolution. [17] The rapid evolution of the disease has made it difficult to estimate its age without the comparison, [16] and SIV has previously been estimated to be a relatively young disease. [18] The link has allowed estimations to be made about the development and age of HIV. [18]

Related Research Articles

<span class="mw-page-title-main">Equatorial Guinea</span> Country in Central Africa

Equatorial Guinea, officially the Republic of Equatorial Guinea, is a country on the west coast of Central Africa, with an area of 28,000 square kilometres (11,000 sq mi). Formerly the colony of Spanish Guinea, its post-independence name refers to its location near both the Equator and in the African region of Guinea. As of 2021, the country had a population of 1,468,777, over 85% of whom are members of the Fang people, the country's dominant ethnic group. The Bubi people, indigenous to Bioko, are the second largest group at approximately 6.5% of the population.

<span class="mw-page-title-main">Malabo</span> Capital of Equatorial Guinea

Malabo is the capital of Equatorial Guinea and the province of Bioko Norte. It is located on the north coast of the island of Bioko. In 2018, the city had a population of approximately 297,000 inhabitants.

<span class="mw-page-title-main">Bushmeat</span> Meat hunted in tropical forests

Bushmeat is meat from wildlife species that are hunted for human consumption. Bushmeat represents a primary source of animal protein and a cash-earning commodity in poor and rural communities of humid tropical forest regions of the world.

<span class="mw-page-title-main">Mandrill</span> Species of Old World monkey from Africa

The mandrill is a large Old World monkey native to west central Africa. It is one of the most colorful mammals in the world, with red and blue skin on its face and posterior. The species is sexually dimorphic, as males have a larger body, longer canine teeth and brighter coloring. It is the largest monkey in the world. Its closest living relative is the drill, with which it shares the genus Mandrillus. Both species were traditionally thought to be baboons, but further evidence has shown that they are more closely related to white-eyelid mangabeys.

<i>Mandrillus</i> Genus of Old World monkeys

Mandrillus is a genus of large Old World monkeys distributed throughout central and southern Africa, consisting of two species: M. sphinx and M. leucophaeus, the mandrill and drill, respectively. Mandrillus, originally placed under the genus Papio as a type of baboon, is closely related to the genus Cercocebus. They are characterised by their large builds, elongated snouts with furrows on each side, and stub tails. Both species occupy the west central region of Africa and live primarily on the ground. They are frugivores, consuming both meat and plants, with a preference for plants. M. sphinx is classified as vulnerable and M. leucophaeus as endangered on the IUCN Red List of Threatened Species.

<span class="mw-page-title-main">African palm civet</span> Species of carnivore

The African palm civet, also known as the two-spotted palm civet, is a small feliform mammal widely distributed in sub-Saharan Africa. It is listed as least concern on the IUCN Red List.

<span class="mw-page-title-main">Cross–Sanaga–Bioko coastal forests</span> Tropical forest ecoregion of west-central Africa

The Cross–Sanaga–Bioko coastal forests are a tropical moist broadleaf forest ecoregion of west-central Africa. This is a lush forest, rich in flora and birdlife.

The Lower Guinean forests also known as the Lower Guinean-Congolian forests, are a region of coastal tropical moist broadleaf forest in West Africa, extending along the eastern coast of the Gulf of Guinea from eastern Benin through Nigeria and Cameroon.

<span class="mw-page-title-main">Cameroon line</span> Chain of volcanoes in the Gulf of Guinea

The Cameroon line is a 1,600 km (1,000 mi) long chain of volcanoes that includes islands in the Gulf of Guinea and mountains on the African mainland, from Mount Cameroon on the coast towards Lake Chad on the northeast. They form a natural border between eastern Nigeria and the West Region of Cameroon. The islands, which span the equator, have tropical climates and are home to many unique plant and bird species. The mainland mountain regions are much cooler than the surrounding lowlands, and also contain unique and ecologically important environments.

<span class="mw-page-title-main">Black colobus</span> Species of Old World monkey

The black colobus, or satanic black colobus, is a species of Old World monkey belonging to the genus Colobus. The species is found in a small area of western central Africa. Black colobuses are large, completely covered with black fur, and like all other Colobus monkeys, do not have a thumb. The species has faced large declines in population due to habitat destruction and hunting by humans, and was consequently listed as Vulnerable on the IUCN Red List in 1994.

<span class="mw-page-title-main">Cameroonian Highlands forests</span>

The Cameroonian Highlands forests, also known as the Cameroon Highlands forests, are a montane tropical moist broadleaf forest ecoregion located on the range of mountains that runs inland from the Gulf of Guinea and forms the border between Cameroon and Nigeria. This is an area of forest and grassland which has become more populous as land is cleared for agriculture.

<span class="mw-page-title-main">Wildlife of Cameroon</span>

The wildlife of Cameroon is composed of its flora and fauna. Bordering Nigeria, it is considered one of the wettest parts of Africa and records Africa's second highest concentration of biodiversity. To preserve its wildlife, Cameroon has more than 20 protected reserves comprising national parks, zoos, forest reserves and sanctuaries. The protected areas were first created in the northern region under the colonial administration in 1932; the first two reserves established were Mozogo Gokoro Reserve and the Bénoué Reserve, which was followed by the Waza Reserve on 24 March 1934. The coverage of reserves was initially about 4 percent of the country's area, rising to 12 percent; the administration proposes to cover 30 percent of the land area.

<span class="mw-page-title-main">Collared mangabey</span> Species of Old World monkey

The collared mangabey, also called red-capped mangabey and white-collared mangabey, is a species of primate in the family Cercopithecidae of Old World monkeys. It formerly included the sooty mangabey as a subspecies. As presently defined, the collared mangabey is monotypic.

<span class="mw-page-title-main">Red-eared guenon</span> Species of Old World monkey

The red-eared guenon, also called red-eared monkey or russet-eared guenon, is a primate species in the family Cercopithecidae. It is native to subtropical and tropical moist lowland forests in Cameroon, Equatorial Guinea and Nigeria. It is listed as Vulnerable on the IUCN Red List and is threatened by habitat loss, illegal bushmeat hunting and pet trade.

<span class="mw-page-title-main">Pennant's colobus</span> Species of Old World monkey

Pennant's colobus or Pennant's red colobus is a species of tree-dwelling primate in the family Cercopithecidae. It is endemic to tropical Central Africa. Three subspecies have traditionally been recognised but its distribution is peculiarly disjunct and has been considered a biogeographical puzzle, with one population on the island of Bioko, a second in the Niger River Delta in southern Nigeria, and a third in east-central Republic of Congo. It is found in rainforests and marshy forests. It is threatened by habitat loss and hunting for bushmeat.

<span class="mw-page-title-main">Preuss's red colobus</span> Species of Old World monkey

Preuss's red colobus is a red colobus primate species endemic to the Cross-Sanaga Rivers ecoregion. An important population occurs in Korup National Park, Southwest Province, Cameroon, but the species' distribution is localized. The species is considered present in adjacent Cross River National Park - Oban Division in Nigeria and hunter reports suggest that few groups remain in Nkwende Hills and Nta Ali Forest Reserve in the broader Korup region. A population is also present in Ebo forest, Littoral Province of Cameroon.

<span class="mw-page-title-main">Atlantic Equatorial coastal forests</span>

The Atlantic Equatorial coastal forests, also known as the Congolian coastal forests, are a tropical moist broadleaf forest ecoregion of Central Africa, covering hills, plains, and mountains of the Atlantic coast of Cameroon, Equatorial Guinea, Gabon, Republic of the Congo, Angola, and Democratic Republic of the Congo.

<span class="mw-page-title-main">Luba Crater Scientific Reserve</span> Protected area of Bioko, Equatorial Guinea

The Gran Caldera de Luba Scientific Reserve is a protected area of 51,000 hectares on the volcanic island of Bioko, a part of Equatorial Guinea. The dense rainforest is rich in plant and animal species including a high population of primates, some endemic to the reserve. Much of the reserve consists of pristine forest. However, the primate population is under threat due to growing demand for bushmeat coupled with lack of enforcement of the ban on hunting in the reserve.

<span class="mw-page-title-main">Bioko</span> Northern island of Equatorial Guinea, Central Africa

Bioko is an island of Equatorial Guinea. It is located 32 km (20 mi) south of the coast of Cameroon, and 160 km (99 mi) northwest of the northernmost part of mainland Equatorial Guinea. Malabo, on the north coast of the island, is the capital city of Equatorial Guinea. Its population was 335,048 at the 2015 census and it covers an area of 2,017 km2 (779 sq mi). The island is part of the Cameroon line of volcanoes and is located off the Cameroon coast, in the Bight of Biafra portion of the Gulf of Guinea. Its geology is volcanic; its highest peak is Pico Basile at 3,012 m (9,882 ft).

<span class="mw-page-title-main">Drill (animal)</span> Species of primate

The drill is a primate of the family Cercopithecidae, related to baboons and even more closely to mandrills.

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