(F. Cuvier, 1807)

(Eng) Drill

(Fre) Drill

Formerly included in Papio, Mandrillus was considered a full genus by Groves (1989). Three subspecies are currently recognised: M. l. leucophaeus, M. l. mundamensis (Mainland drill) and M. l. poensis (Fernando Po drill).

Wherever it occurs, the drill is threatened by loss of habitat as well as by hunting and is listed as Endangered (EN: criteria A1acd+2cd, C1+2a), both at the level of species as a whole and as M. l. mundamensis and (criteria B1+2abcde, C1) as M. l. poensis, while M. l. leucophaeus is considered Vulnerable (VU: criteria A1acd+2b).

Literature available on the ecology of this species is limited. Notes on the main aspects of its ecology are reported in Gartlan (1970). No specific studies on its habitat use and requirements have been carried out. Data on its occurrence on Bioko Island can be found in Butynski & Koster (1994), while the overall species’ distribution is analysed in Grubb (1973), Hall (1966) and Oates (1988). The authors mentioned above also include some notes on the species’ ecology. Blom et al. (1992) discuss the possible presence of the drill in Gabon. General information on its ecology is found in Bourlière (1985), Kingdon (1997) and Stuart & Stuart (1997). Status, threats, and conservation issues are discussed in Gadsby et al. (1994), Lee et al. (1988), Oates (1994, 1996).

Known extent of occurrence

Distribution of the drill is still uncertain, but it appears to have a very restricted range in western Cameroon (north of the Sanaga River), southeast Nigeria and Bioko Island (Eq. Guinea). Occasional reports of drills in Gabon have almost certainly been caused by confusion with immature or adult female mandrills, as the two species are not sympatric (Harrison, 1988). The distribution map shown in Fig. 2.3.28.a was acquired from Oates (1996) and verified to match the river network; it might still be too optimistic with regard of the species’ true range, since few tracts of unpopulated rain forest remain. For example in Nigeria M. leucophaeus is known only from isolated mountain patches near the Afi River on the border with Cameroon (Lee et al., 1988). A detailed and updated distribution map is also given in Gadsby et al. (1994); according to it, its occurrence is restricted to small fragments of suitable habitat, which are isolated by barriers such as major roads, human settlements and cultivations.

A predominantly rain forest species, it can also be found in forest savanna mosaics. It is never seen near crops (Butynski & Koster, 1994; Lee et al., 1988).

Based on these environmental preferences, the following scores were assigned (Fig. 2.3.28.b) (2.3.28.a):

The output of the probabilistic-continuous (PC) distribution model is shown in Fig. 2.3.28.c.

The known EO, as drawn in Fig. 2.3.28.a, appears to be too optimistic and the AO should be considerably more restricted. Suitable areas appear to make up only 47% of the EO. Besides the obvious fragmentation due to the presence on Bioko, the mainland distribution is also scattered over several smaller fragments (LPI = 46.98%). The CD and PC models show a complex mosaic of areas of different suitability, and human disturbance and persecution further threaten the species’ survival. The accordance of the CD model to the results of field work is 57.14%, which indicates that the model represents the species’ distribution sufficiently well. About 6% of the total AO (but only 3% of the most suitable areas) appears to be included in existing protected classes: this small percentage cannot possibly offer sufficient protection to this highly endangered species.