Drills are among Africa’s most endangered mammals, and are listed by the IUCN as the highest conservation priority of all African primates. They are semi-terrestrial monkeys, exhibiting extreme sexual dimorphism with males weighing up to 45 kg – three times the size of females. They are semi-nomadic seasonally and little is known of their behavior or ecology in the wild. Their closest relative is the mandrill Mandrillus sphinx, found from southern Cameroon through mainland Equatorial Guinea (Rio Muni), Gabon and into Congo. The two species are allopatric across the Sanaga River. On Bioko drills occur as unique subspecies Mandrillus leucophaeus poensis. Drills are found only in Cross River State, Nigeria; south-western Cameroon; and on Bioko Island, Equatorial Guinea. Their entire world range is less than 40,000 km2, smaller than Switzerland. Drill numbers have been declining in all known habitat areas for decades as a result of illegal commercial hunting, habitat destruction, and human development: as few as 3,000 drills may remain in the wild, the highest population estimate is 8,000. Safeguarded, however little real protection exists for drills or other endangered species that share their habitat. Drills will only survive the present and into the long term by the grace of their human neighbours, and the will and commitment of their host governments to enforce existing laws. As habitats shrink and become increasingly fragmented, the interactive management of wild and captive populations may play a crucial role.
There are two monotypic species in the genus Mandrillus, the mandrill (M. sphinx) and the drill (M. leucophaeus), each with no subspecies (Groves 2005).
Suborder: Haplorrhini Infraorder: Simiiformes Superfamily: Cercopithecoidea Family: Cercopithecidae Subfamily: Cercopithecinae Genus: Mandrillus Species: M. leucophaeus, M. sphinx
M. sphinx inhabits mainly tropical rain forests (including semi-deciduous lowland rainforest, closed-canopy lowland moist forest, and other primary and secondary rainforests often with very dense vegetation) and forest-savannah mosaic forests (never moving far into pure savannah), but also Marantaceae and rocky forest, as well as gallery forest within savannah areas, riparian forests, agricultural areas and even inundated forests and stream beds (Sabater Pí 1972; Hoshino et al. 1984; Hoshino 1985; Lahm 1986; Harrison 1988; Rogers et al. 1996; Tutin et al. 1997a; Matthews et al. 1998; Abernethy et al. 2002; Astaras et al. 2008). They sometimes also cross grassy areas within their forested habitats (Harrison 1988). M. leucophaeus are found in coastal forest, lowland forest, premontane forest, submontane forest, montane forest, and montane savannah, and as high as 2000 meters (6561.7 feet) above sea level (Wild et al. 2005; Astaras et al. 2008). At the Korup National Park (KNP), Cameroon, a habitat of M. leucophaeus, average rainfall is over 500 cm (196.9 in), with a wet season between May and October and a dry season between December and February. Similar to the Lopé Reserve, temperatures are relatively constant throughout the year, with average highs around 30.6°C (87.1°F) (Astaras et al. 2008). In many ways, the often dense habitats of the genus Mandrillus have made research difficult, and as a result, little is known about certain aspects of their ecology and behavior (Hoshino et al. 1984; Jolly 2007). These drills also inhabit some parts of the Lebialem-Mone forest landscape. The measure threat faced by these species include habitat fragmentation and poaching. These activities for the locals of some communities constitute the most accessible route of income generation.
