The Bioko drill (Mandrillus leucophaeus poensis ) is a subspecies of the drill, an Old World monkey. It is endemic to Bioko Island, Equatorial Guinea, located off the west coast of Africa. The drill is one of the largest monkey species, and is considered endangered. 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. The capital of Equatorial Guinea, Malabo, is on Bioko Island. The Malabo market is the primary point of sale for bushmeat on Bioko Island. 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. The commercialisation of hunting on Bioko Island has made this practice unsustainable. 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 and hunting remains the largest threat to the drill's population.
A frugivore is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts, and seeds. Approx...
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TerrestrialTerrestrial animals are animals that live predominantly or entirely on land (e.g., cats, ants, snails), as compared with aquatic animals, which liv...
Among animals, viviparity is the development of the embryo inside the body of the parent. The term 'viviparity' and its adjective form 'viviparous'...
Highly social animals are those which are highly interactive with other members of their species. They live in large groups, nest in colonies, and ...
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Not a migrantAnimals that do not make seasonal movements and stay in their native home ranges all year round are called not migrants or residents.
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starts withThe Bioko drill is of a similar appearance to the mainland drill, with a green-brown coat and white fur on the underbelly. 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. 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. 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. The males have a shiny black face with sharp features, and an elongated muzzle. They are further distinguished by purple, blue and red hair on their rump and a white fur on their chin.
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. While the Bioko drill will preferentially inhabit lowland forests, tending to larger groups in these areas, populations have been found inhabiting areas up to 2,000m above sea level in grasslands and areas with dense undergrowth. Lowland populations tend to be more diverse, potentially due to a higher diversity of vegetation, with fruits more prevalent at lower altitudes and higher altitudes more conducive to more fibrous sources of food such as herbs and ferns.
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. The inaccessibility of these regions for hunters allows the drills to reach greater populations without hunting pressure. However, there is rapid road and infrastructure development that may put these populations at further risk. 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. This also poses an issue to habitat range of the Bioko drill as their population density is lowest around roads.
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. They are highly social animals that live in groups of around 20, or even up to 30 individuals, predominantly made up of adult and adolescent females. They are also highly vocal and are easy to track through their callings. The Bioko drill will also respond to distress bleats from duikers. While they spend most of their time on the forest floor during the day, they tend to sleep in trees.
The Bioko drill is a primarily terrestrial monkey, and will forage in groups for several hours a day on the forest floor, though they will quickly climb trees when threatened by hunting dogs. 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. The Bioko drill is also known as a primary seed disperser, contributing to tree dispersal through their consumption of tree seeds and fruits. 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. The hunting of the Bioko drill has been correlated with a loss of hardwood trees and sapling undergrowth. Recent observations have seen the drills move from preferentially eating fruits to consuming more herbaceous material due to hunting pressures. 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.
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. 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. They are also capable of husking coconuts to consume them. The drill diet may also consist of wood and mushrooms, the latter of which is rare in a primate. 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, and the African giant snail. In one instance, the remains of rodents and frogs were found in faecal matter of a drill, and they have also been noted to forage for marine turtle eggs on beaches. Additionally, the drill's response to distress calls of duikers may be indicative of their willingness to consume them.
While drills are not often observed in or near agricultural areas, they can be considered pests, and shot by farmers to protect crops, particularly by the Bubi, the native people of Bioko, who tend to be predominantly agricultural, and live closer to greater populations of the drill.
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, as the lowland habitats are conducive to larger groups of drills, and are generally preferred.
There is some evidence that Bioko drills captured from the wild may used in circuses. 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 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.
Social animals are those animals that interact highly with other animals, usually of their own species (conspecifics), to the point of having a rec...