Philantomba congica (Lönnberg, 1908)

Don E. Wilson & Russell A. Mittermeier, 2011, Bovidae, Handbook of the Mammals of the World – Volume 2 Hoofed Mammals, Barcelona: Lynx Edicions, pp. 444-779 : 713

233.

Western Blue Duiker

Philantomba congica

French: Céphalophe du Congo / German: Kongo-Blauducker / Spanish: Duiker azul occidental

Other common names: Congo Blue Duiker

Taxonomy. Cephalophus nyasae congicus Lonnberg, 1908 ,

Congo.

Formerly considered to be a subspecies of P. monticola . Monotypic.

Distribution. Nigeria (E of Cross River) to W Central African Republic and DR Congo (E to Lisala), S to coastal S Republic of the Congo; distribution is bordered to the S by the Congo River.

Descriptive notes. Head—body 56-66 cm, tail 8 cm, shoulder height 32-38 cm; weight 4-6 kg (3.9-5 kg) in males and 5-4 kg (4:2.6-1 kg) in females. Overall coloration is a warm grayish-brown, paling to gray on the flanks. The dorsum is especially dark, and may approach black in some individuals. A distinct black horizontal band crosses the haunches at the base of the tail, contrasting strikingly with the very pale brown rump and thighs. This contrast decreases cranially as both the pale and dark markings merge gradually with the overall coloration. The undersides are white. The tail is black above and white underneath. The legs are gray or brownish-gray; the degree of brownness tends to increase in eastern parts of the species’ distribution. Dark marks are present above the hooves. A reversal of hair is seen on the nape of the neck in roughly one-half of specimens. The face is dark, with reddish cheeks. Simple, spike-like horns are present in both sexes; they are typically 2-8—4-48 cm in males and 2-36.2-98 cm in females. Dental formulais10/3, C0/1,P 3/3, M 3/3 (x2) = 32.

Habitat. The Western Blue Duiker inhabits a wide range of forested habitats, including high forest, secondary forest, and forest edges. Large open areas are avoided, but pockets of gallery forest within the savannas of Cameroon are used. Mixed forests appear to be preferred over monodominant forests, and dense vegetation at ground level negatively affects abundance. The Western Blue Duiker enters dense thickets only if alarmed; even resting spots are often in areas with minimal underbrush. Population densities are highly variable. Low estimates include 0-9-6-1 ind/km?® in Lopé National Park, Gabon, and 6:4-8-2 ind/km?in Korup National Park, Cameroon. Net hunts in south-western Central African Republic resulted in density estimates of 10-7-45-9 ind/ km?. In north-eastern Gabon, densities as high as 62-78 ind/km* may be reached.

Food and Feeding. Frugivorous. Stomach content analysis of 16 animals in Gabon revealed that fruits and seeds constitute 78-:4% of the diet, with seeds distinctly preferred. The remainder of the diet includes 20-3% leaves and stems and small amounts (less than 1%) of flowers, fungi, and animal matter. Preferred fruit species include Artabotrys letestui, Coelocaryon preussii (or Pycnanthus angolensis ), and Staudtia stipitata. Other species observed in the diet include Pseudospondias longifolia, Canarium schwein-Sfurthu, Hugonia spp., Rytigyniasp., Gambeya beguei, and Donella pruniformis. Western Blue Duikers are able to swallow food items as large as 2-2 cm; if possible, seeds are generally chewed and crushed prior to swallowing. Most foliage consumed is in the form of fallen leaves picked from the forest floor; juveniles tend to consume more leaves and less fruit than adults. Western Blue Duikers will occasionally stand on their hindfeet to reach tall vegetation, but this is not sustained for long unless the front feet can rest on something for support. This species has been observed consuming ants by licking them from the substrate.

Breeding. Breeds year-round, but with peaks in birth rates during the two dry seasons (centered around January and July). A male courts a female by pursuing her,licking at her tail region during the chase. Ritualized foreleg kicks “laufschlag” are practiced by the male prior to copulation. Estrus lasts for approximately 24 hours, during which time the male pursues the female frequently and is quite aggressive to other animals in the vicinity. Flehming is frequently performed by males when females urinate (approximately 87-5% of cases); this inconspicuous lip curl generally lasts for 10-3 seconds. Gestation is approximately 204 days, after which a single offspring is born. Maturity is reached at 1-2 years; subadults disperse at this time for social (rather than resource-based) reasons, with females typically dispersing earlier than males. Dispersal distances are generally short (a few hundred meters) if unoccupied habitat is present, but distances of 1-5 km from the natal home range have also been recorded. Life span may exceed twelve years in captivity.

Activity patterns. Strictly diurnal. The activity patterns of Western Blue Duikers are closely associated with cycles of light and dark. Activity typically begins at 05:30-06:00 h and will continue sporadically throughout the day until 18:00-19:00 h. Activity shows a bimodal pattern, with a peak during the early morning (06:00-08:00 h) and late afternoon (16:00-18:00 h). The decreased level of activity during midday is the result of two or three rests between foraging bouts; these occur most frequently between 09:00 h and 14:00 h. Western Blue Duikers are generally active (moving or foraging) for 67-76% of daylight hours. Activity may be extended into the evening (until 20:00-21:00 h) during periods of excitement, such as estrus. At night, Western Blue Duikers retire to regularly used resting places; such resting spots are often smelled and scraped at briefly with the hooves before the duiker lies down. Occasionally, resting spots are changed during the night (typically involving a movement of several meters), but more often individuals will simply rise to stretch and groom before lying back down. Activity tends to be higher during the dry seasons, as reduced food resources require increased foraging time.

Movements, Home range and Social organization. The typical social unit is a bonded adult pair (one male and one female), sometimes accompanied by one or two subadult offspring. Partners spend approximately 54% of their active time together. In southern Gabon, pairs are only seen in 20% of observations, but this may be reflective of the poorvisibility in dense habitats. Night-time resting places are shared by pairs about 75% ofthe time. Allogrooming among pairs focuses on the ears, forehead, and preorbital glands—all areas that are difficult to self-groom. Partners also mark each other with their preorbital glands, especially on the forelegs, lower rear legs, face, and rump. The female of the pair usually leads when moving (in 92% of 215 observations). Daily linear movements average approximately 1 km (65-1770 m). While active, Western Blue Duikers constantly flick their tails up and down, flashing the white underside; this is thought to serve as a contact signal. Soft, brief calls also help maintain contact between family members. Pairs occupy stable home ranges. There are few changes in either boundaries or occupants across years, although movements tend to be less dispersed during the dry seasons. Typical home ranges are 0-02-0-04 km? up to 0-06 km? the size does not appear to be affected by the sex or age of the occupants. Home ranges do not overlap between neighbors. Both sexes appear to be territorial, each defending the area against others of the same sex. Natural boundaries often form the territory edges; the borders are marked with horn scrapings on tree trunks and with scent marks. Preorbital gland secretions are left on vertical surfaces (especially tree trunks and branches) at head-height; the secretion is clear and odorless, but accumulates as a white paste on frequently marked areas. Scent marking is most frequently performed by males (5-7 times/hour). Urine and feces are deposited across the home range, and may indicate that an area is occupied. The core area of each territory tends to be used more than the periphery, although daily movements usually include a patrol of the boundaries to reestablish border markings. Males have been recorded making frequent short forays (100-300 m) outside of their territories; however, the core of adjacent home ranges remains exclusive. Males may also leave when a female gives birth; the regular pattern of bonding may not be returned to for several weeks. When confronted with a potential threat (usually detected by sight or hearing), Western Blue Duikers freeze in position, tensing the body; the head may be moved vertically or horizontally to better assess the situation. A loud whistle is used as an alarm call, and is produced just before and during flight; the hindfeet may also be stomped just prior to fleeing. The Western Blue Duiker rarely flees far, usually stopping among dense vegetation after several meters to reassess the threat. Members of family groups will all flee in response to an individual’s alarm call, but usually run in different directions. In areas with heavy hunting by humans, Western Blue Duikers flee immediately without the observation phase.

Status and Conservation. CITES Appendix II (under P. monticola ). Classified as Least Concern on The IUCN Red List (combined with the other nine blue duiker species within the P. monticola complex). The Western Blue Duiker is the most commonly hunted duiker species in Cameroon;it is also the most frequently captured animal in south-western Central African Republic, accounting for 31% of carcasses and 16% of biomass. This species is currently abundant in many protected areas and common in unprotected areas within its range. Populations may be declining in areas of heavy human habitation due to intense hunting for bushmeat.

Bibliography. Croes et al. (2007), Dubost (1980, 1983, 1984), Dubost & Feer (1992), East (1999), Feer (1995), Grubb & Groves (2001), IUCN/SSC Antelope Specialist Group (2008as), Lydekker (1914), Mockrin (2010), Noss (1998a, 1998b), Waltert et al. (2006), Weigl (2005), Wilson (2001).

Figures

233. Western Blue Duiker (Philantomba congica), 234. Bioko Blue Duiker (Philantomba melanorhea), 235. Eastern Blue Duiker (Philantomba aequatorialis), 236. Mountain Blue Duiker (Philantomba lugens), 237. Simpson’s Blue Duiker (Philantomba simpsoni), 238. Malawi Blue Duiker (Philantomba hecki), 239. Zimbabwe Blue Duiker (Philantomba bicolor), 240. Cape Blue Duiker (Philantomba monticola), 241. Angolan Blue Duiker (Philantomba anchietae), 242. Zambian Blue Duiker (Philantomba defries)

Distribution. Nigeria (E of Cross River) to W Central African Republic and DR Congo (E to Lisala), S to coastal S Republic of the Congo ; distribution is bordered to the S by the Congo River.