Mandrillus leucophaeus (F. Cuvier, 1807)

Russell A. Mittermeier, Anthony B. Rylands & Don E. Wilson, 2013, Cercopithecidae, Handbook of the Mammals of the World – Volume 3 Primates, Barcelona: Lynx Edicions, pp. 550-755 : 655

31.

Drill

Mandrillus leucophaeus

French: Drill / German: Drill / Spanish: Dril

Other common names: Bioko Drill (poensis), Mainland Drill (leucophaeus)

Taxonomy. Simia leucophaea F. Cuvier, 1807 ,

Africa.

Bioko Island is just 30 km offshore and believed to have been connected to the mainland as recently as 10,000 years ago. Two subspecies recognized.

Subspecies and Distribution.

M.l.leucophaeusF.Cuvier,1807—fromtheCrossRiverinSENigeria,EtotheSanagaRiveranditstributarytheMbamRiverinWCameroon;inlandfromthecoast,the distributionislimitedtotheNbythederivedsavannaboundary.

M. l. poensis Zukowsky, 1922 — Bioko I.

Descriptive notes. Head-body 72-83 cm (males) and 45.5-50 cm (females), tail 8-6— 12:5 cm (males) and 5.9-4 cm (females); weight 14.5-27 kg (males) and 6.5-12 kg (females). The Drill has extreme sexual dimorphism; weight of adult males is more than twice that of adult females. The distinctive smooth, bare, black face, with paranasal ridges, in both sexes is moon-shaped and greatly enlarged in males. Edges of the black face are sharply demarcated by white skin, giving a dramatic, mask-like appearance. Fully adult males bear a bright red strip between the black lower lip and white chin. Drills have white chin hairs without beard in adults and whiskers in males. Ears are naked, and black; bare skin behind ears is white and prominently visible in males. Forehead and crown are dark brown to blackish. Males have a semi-erectile crest, and the mantle of the neck and shoulder hair look like a short mane. Body hairis light brown to tawny gray, ventral hairs paler to white, with a faint brown dorsal stripe in adult males. Lower limbs are darker. Both sexes have a sternal scent gland; adult males have a pectoral tuft that holds aromatic secretions. Hands and feet are black. Ventral skin is white, and dorsal skin is blue-gray. Adult male Drills have a spectacular rump coloration exposed by sparse hair, displaying a deep spectrum from hot pink to lavender and blue, depending on age and condition. In both sexes,ischial callosities are pale pink. Skin around the anus and female sexual skin to the tail are red to pink. Adult males have a prominent heavy jaw and impressive canines; upper canines may exceed 5 cm. Females and males up to four years of age appear similar. Neonates have white to pink skin on face, ears, hands, and feet; they have silvery-gray hair and black “infant caps.” Infant pelage is replaced gradually over 3-6 months to eventually resemble color of adult females. Face darkens to black by 4-6 months. The “Bioko Drill ” (M. I. poensis) is smaller and less sexually dimorphic than the Mainland Drill (M. I. leucophaeus ). Relative to the Mainland Drill , the skull of the Bioko Drill is shorter and broader, overall stature is slightly less, and hair color may be less tawny and more blackish.

Habitat. Closed forest from coastal lowland to transitional and semi-montane forest further inland. These areas give way to forest-savanna mosaic and high-elevation grassland with gallery forest where Drills are absent. In the 1930s, I. T. Sanderson collected Drills in mixed grassland—gallery forest of Cameroon’s Bamenda Highlands, but these forests have now been largely eliminated. Across their limited distribution, there is a single long dry season in December—March; Bioko Island is wetter.

Food and Feeding. Drills are omnivorous, opportunistic, wide-ranging foragers. Fruits and seeds dominate their diets; other plant material includes blossoms, leaves, stems and pith, forbs, grass blades, corms, roots, tubers, and bark. Animal matter includes adult and larval insects and other invertebrates such as crabs and snails, bird and reptile eggs, small fish, reptiles, and amphibians. Drills will kill small birds and mammals; feathers, hair, and bone have been found in feces in the wild. They also eat mushrooms. Drills forage mostly on the ground, with some individuals feeding in the trees above. Younger animals are more aptto forage in the trees because their greater mobility and smallersize allow them to gain access to small branches, thereby reducing competition. Drills are avid diggers, scraping the forest floor, shifting leaflitter and other detritus, and breaking open rotten logs, branches, and insect mounds Their foraging leaves a distinctive sign of a group’s passing. Drills readily enter shallow water to capture tadpoles and other aquatic foods, and they dig up marine turtle eggs on Bioko Island beaches. Studies in Korup National Park, Cameroon, found that fruits and seeds comprised more than 82% of the diet by weight, depending of the season. Insects or other animal matter was 5:5%.

Breeding. Female Drills exhibit a prominent sexual swelling and cycle throughout the year; mean cycle length is 33 days. A single infant is born; twins are very rare. The mean gestation period is 176 days; 72% of births occur in the rainy season with nearly 50% of births in the two peak rainy months (June and July). A female may reproduce every year and will not actively wean her infant until her next infant is delivered. Females enter puberty at three years of age and typically beartheir first offspring at four years. Males are sexually mature at five years of age and will double in size before reaching full maturity at 8-10 years. These reproductive data are derived from more than 400 births at the Drill Ranch project in Nigeria, where Drill groups live in multi-hectare, electric fenced enclosures of natural habitat. The dominant male is believed to sire most offspring in his group.

Activity patterns. By day, a Drill group moves through the forest, foraging on the ground and in the lower levels of trees. They may rest or otherwise reduce travel and active foraging in the early afternoon. Before dusk, the group ascends a single large tree or multiple trees in close proximity, where some feeding and movements continue. There is no distinctive male loud call at this time, but contact calls between mothers and their young are heard. By nightfall, each Drill has selected a sleeping site from 10 m upward to tree crowns and the group is quiet. Infants sleep with their mothers. By dawn, contact calls and movements commence followed by urination and defecation; soon after, the group descends and assembles to begin its day’s activities.

Movements, Home range and Social organization. It is unclear if groups of Drill maintain a fixed home range or move across a larger area in semi-nomadic, seasonal patterns. Much anecdotal evidence and some field observations indicate Drills roam the forest in semi-regular, annual patterns, perhaps following fruiting trees or other food and water availability. Study sites in Korup and Ebo national parks have found Drills throughout the year. Drills may range more widely in less resource rich areas, such as higher elevation or marginal forests. Social organization data are limited and somewhat speculative. Drills live in multimale-multifemale groups with a dominant male. Typical group sizes are 15-30 individuals, with roughly a 1:2 ratio offully adult males to the rest of group. “Supergroups” of 100 individuals or more may be temporary fusions of typical, dominant-male units. Supergroup formation may be seasonal and function as an opportunity for individuals to transfer between groups. Solitary Drills are uncommon, with only adult males observed alone.

Status and Conservation. CITES Appendix I. Classified as Endangered on The IUCN Red List, including both subspecies. The Drill is listed as Class B in the African Convention on the Conservation of Nature and Natural Resources. With a small natural distribution of less than 50,000 km?in parts of three countries, the Drill’s statusis precarious. Within this distribution, less than 20,000 km? are usable for Drills and fragmented into at least eleven “habitat islands” on the mainland and two on Bioko Island. These restricted areas have a relatively high human density and several large urban centers that fuel the demand for bushmeat. Hunters may use dogs, whereby a group of Drills can be treed and several of them shot in a single hunting encounter; verified reports of up to 25 such kills exist. Commercial hunting for the last 30 years has greatly reduced the numbers of Drills. Habitat is lost primarily to farming but also to illegal logging in Nigeria and to farming and industrial logging in Cameroon. Large areas were cleared for palm, banana, and rubber plantations in Cameroon in early colonial days, and a recent upsurge in palm plantation proposals threaten important core habitat of Drills and other wildlife. Roads and further fragment habitat and ease access for hunters, bushmeat traders, farmers, and timber poachers. Drills are well protected by law from hunting and trade in all three countries where they occur, but enforcementis poor or absent. In Nigeria, most remaining habitats are technically protected in the two discontinuous divisions of the 3440 km* Cross River National Park; additional protected habitats include the smaller Afi Mountain Wildlife Sanctuary (100 km?*) and Mbe Mountain community forest (80 km?). Cameroon contains ¢.75% of the Drill’s remaining habitat. Korup National Park covering 1259 km? is the earliest protected area and is the core of the Drill’s current distribution. New and proposed protected areas include Takamanda, Ebo, Mount Cameroon, and Bakossi national parks. Banyang-Mbo Wildlife Sanctuary and numerous forest reserves nominally protect additional habitat but do not control hunting. Most protected areas form landscape blocks with contiguous forest reserves and community forests, and some across the Nigeria—Cameroon border. On Bioko Island, Drill habitat is protected in Basilé National Park (330 km?) and Luba Caldera Scientific Reserve (510 km?); these areas cover more than 40% ofthe island. Drills are protected in part of Luba Caldera but may already be extirpated in Pico Basilé. Despite existing and planned habitat protection in all countries where the Drill occurs, the control of hunting is inadequate. As groups and subpopulations shrink and become increasingly isolated from one another, Drills may be unable to form supergroups and may lose viability. Population estimates are less than 10,000 individuals and possibly as low as 4000. A large managed population of captive Drills living in semi-wild conditions in Nigeria is prepared for group reintroduction to reinforce local subpopulations if needed.

Bibliography. Astaras (2009), Astaras & Waltert (2010), Astaras et al. (2011), Butynski & Koster (1994), Butynski et al. (2009), Caldecott et al. (1996), Cronin et al. (2010), Disotell et al. (1992), Elton & Morgan (2006), Fleagle & McGraw (2002), Gadsby (1990, 2002, 2006), Gadsby & Jenkins (1997/1998), Gartlan (1970), Gartlan & Struhsaker (1972), Gonzalez-Kirchner & de la Maza (1996), Grubb (1973), Hearn & Morra (2001), Hearn et al. (2006), Hill (1970), Linder (2008), Marty et al. (2009), Morgan & Astaras (2008), Napier (1981), Oates (1996b, 2011), Sanderson (1940), Schaaf et al. (2013), Steiner et al. (2002/2003), Waltert et al. (2002), Wild et al. (2005), Wood (2007), Zukowsky (1922).

Figures

On following pages: 16. Arunachal Macaque (Macaca munzala); 17. Tibetan Macaque (Macaca thibetana); 18. Stump-tailed Macaque Macaca arctoides); 19. Long-tailed Macaque (Macaca fascicularis); 20. Rhesus Macaque (Macaca mulatta); 21. Japanese Macaque (Macaca fuscata); 22. Taiwanese Macaque (Macaca cyclopis).

Subspecies and Distribution. M.l.leucophaeusF.Cuvier,1807—fromtheCrossRiverinSENigeria,EtotheSanagaRiveranditstributarytheMbamRiverinWCameroon;inlandfromthecoast,the distributionislimitedtotheNbythederivedsavannaboundary. M. l. poensis Zukowsky, 1922 — Bioko I.