Tragelaphus bor, Heuglin, 1877

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 : 598-599

20.

Nile Bushbuck

Tragelaphus bor

French: Guib du Nil / German: Sudan-Schirrantilope / Spanish: Bushbuck del Nilo

Taxonomy. Tragelaphus bor Heuglin, 1877 ,

Bor, on the White Nile, Bahr-el-Ghazal.

The Nile Bushbuck was formerly considered a subspecies of T. scriptus , but it is diagnostically different from other bushbucks. The mtDNA support for this clade is 90%. Apparently, there is, or was, gene flow between bor and sylvaticus in the southern part of Queen Elizabeth National Park, south-western Uganda, which led to the description of the subspecies sassae (here, a synonym of 7. sylvaticus). Bushbucks from the northern part of the Park (the Mweya Peninsula) are considered here to be the Nile Bushbuck. Most of the ecological and behavioral research on bushbucks has been conducted there. Synonyms of the Nile Bushbuck include cottoni , meridionalis , dodingae , locorinae , laticeps , and wellensis . Monotypic.

Distribution. E Central African Republic, extreme NE DR Congo, S Sudan, W Uganda, NW Kenya, and Rwanda. The Nile Bushbuck may range further west than illustrated here because recent genetic analyses by Y. Moodley and colleagues suggest it can occur in all of the Central African Republic and southern Chad. More research is required to clearly establish the ranges of the Nile Bushbuck and the Central Bushbuck ( T. phaleratus ).

Descriptive notes. Head-body 117-145 cm (males) and 114-132 cm (females), tail 19-24 cm, shoulder height 64-100 cm (males) and 61-85 cm (females); weight 40-80 kg (males) and 24-60 kg (females). These measurements are general for the bushbuck group and should be considered provisional until further information is available for individual species. Tragelaphines are typified by their sexual dimorphism, and the weight of male bushbucks, in general, is about 160% that of females. Bushbucks are the smallest tragelaphines, with large ears and eyes and a rather round, crested back. Their hindquarters tend to be higher and more robust that their forequarters. The color of the Nile Bushbuck is more ocher (pale yellowish-brown) with no dark suffusion of the hairs on the neck and less red than the Western Bushbuck (7. scriptus ) and the Central Bushbuck, and the transverse stripes—there are up to ten—are less distinct, especially on old individuals. The dorsal crestis black. The upper longitudinal band is short or absent, and the lower one is generally broken into spots and streaks. Several haunch spots are usually present, along with a white mark on the throat. White markings on the legs are generally well developed. Inguinal glands occur ahead of the mammae, but there are no false hoof glands. The tail is relatively short, long-haired, and bushy, dorsally colored the same as the back, white underneath, and usually tipped in black. Only males have keeled horns, which are nearly straight, generally with only one or slightly more twists. Horn lengths of the Nile Bushbuck are 23-25 cm. Average total length of the skull is 23-8 cm. Dental formulais10/3, C0/1,P 3/3, M 3/3 (x2) = 32. Diploid numbers for the bushbuck group are 33 for males and 34 for females.

Habitat. As a group, bushbucks are the most ubiquitous hoofed mammals in Africa, but because of their relatively solitary nature (particularly males), relatively small size, tendency to freeze and blend into their surroundings, and preference for forest and forest edge, they are difficult to observe and census. Bushbucks are usually found near free water, which may be as much a reflection of their preferred forested habitats thriving near water as a physiological need. The Nile Bushbuck occurs in a variety of habitats and at various elevations. For example, in Volcanoes National Park on the border of Rwanda and the DR Congo, Nile Bushbucks occur in all eight available habitats at elevations of 3100-3600 m, with seasonal variation. Densities in the forested habitat in the saddle between two volcanic craters, estimated from fecal counts, ranged from 38-7 ind/km? in September—-November to 53-6 ind/km? in June-August. In alpine habitat at 3400-3600 m, densities ranged from 8 ind/km? in June-August to 13-6 ind/km? in March-May. On the Mweya Peninsula in Queen Elizabeth National Park in south-western Uganda, forest thickets and grasslands with a preferred woody herbaceous species (Indigofera) were used.

Food and Feeding. Beginning in the early 1970s and continuing to the present, several important investigations on the Nile Bushbuck on the Mweya Peninsula in Queen Elizabeth National Park, south-western Uganda, have added significant ecological and behavioral insights that are probably applicable to many of the bushbuck species. In the late 1970s, Nile Bushbucks there ate 27 herbaceous plants, five shrub species, and three grass species throughout the year; two shrubs, Erythrococcus bongensis and Capparis tomentosa, were eaten in all seasons, but herbaceous plants were preferred during the wet season. During three years of study, dry season diets averaged 59:3% shrubs and 40-7% herbs, and wet season diets averaged 29-9% shrubs and 62-7% herbs. Daily feeding locations were small, wooded, and near water or gullies. In recent years, Nile Bushbucks on the Mweya Peninsula ate 43 plant species with seasonal variation: 18 perennial woody herbs, 13 annual herbs, eight shrub species, two tree species, and two climbing herbaceous plants. Relative to time spent feeding as an index to diet, four plants accounted for the greatest percentage of the diet but varied seasonally: during the wet season, 317% Dichrostachys cinerea (tree), 30-6% Indigofera spp. (perennial woody herb), 11-3% Pavetta albertina (shrub), and 7-2% Fluggea virosa (shrub); during the dry season, the percentages of the diet were 7-8%, 27-3%, 14-:3%, and 14-6%,respectively.

Breeding. Recent and detailed research on the Mweya Peninsula, Uganda, has provided the greatest insights into the breeding characteristics and behavioral repertoire of the Nile Bushbuck to date, but their general applicability to the bushbuck group range-wide remains to be studied and will be a fruitful endeavor for the future. Female Nile Bushbucks are organized in matrilineal clans, and males are territorial. Male Nile Bushbucks display agonistic behavior toward one another throughout the year, in part because breeding can take place at any time. Lateral displays of varying intensity are the most common behavior. Other important behaviors include threat displays (lowand medial-horn presentations), overt aggression (fake attack or low horn-to-horn combat), chasing, and escorting. Escorting was newly described for male Nile Bushbuck on the Mweya Peninsula in 1999-2002; it involves a series of the other behaviors mentioned above coupled with a “pursuit march” while the territorial male escorts another mature male or subadult male from his territory. Female Nile Bushbucks also show aggressive behavior toward each other, most commonly with head butting, snout thrusting, neck winding, and jumping toward another with raised head and ears held back. Mutual grooming is common among females, particularly mothers and their offspring. Mating behaviors of the Nile Bushbuck on the Mweya Peninsula and other bushbuck species are understated relative to other tragelaphines. Courtship by the male involves a form of lateral display without the dorsal crest or tail erect or the back arched, often while uttering an infantlike twittering call. A courting male will approach a female rather quickly in a low-stretch position with his horns held back on his neck, as if to hide them. Females act submissively or defensively depending on their readiness to breed. Genital and urine testing, followed by lip curling of the males, are common. A male may draw alongside the female in a “mating march,” rubbing his cheek and perhaps scent on the female’s hindquarters. As with other tragelaphines, the male rests his chin on the back and hindquarters of the female before mounting. On the Mweya Peninsula in the early 2000s, individual female Nile Bushbucks produced 0-3-1-6 offspring/year, or a mean birth rate of 0-65-0-89 offspring/year. Young bushbucks remain hidden after birth and select their own hiding places. Females determine the timing and frequency of nursing; typically, a female will nurse her young for 5-10 minutes 2-5 times per day. Young are weaned at 4-6 months.

Activity patterns. The Nile Bushbuck displays an alternating pattern of feeding followed by resting/ruminating and can be nocturnal in some areas. In the early 1970s, Nile Bushbucks on the Mweya Peninsula were said to be less active during the day than during the night. Males rested (standing or lying) more during the day (07:00-17:00 h, peaking at 08:00-13:00 h) than females (peaks at 07:00-10:00 h, 13:00-15:00 h, and 17:00-19:00 h). Males fed actively from 23:00 h to 03:00 h. While foraging, Nile Bushbuck tended to remain close to shrubby cover; 52% of bushbuck observations were within five meters of cover. Later studies noted that Nile Bushbucks were equally active day and night and alternated activity periods every 2-5 hours throughout the 24hour cycle. On average, they were active 23-2% of the time and lying, standing, and ruminating 76-8% of the time; no differences were detected between sexes, among age classes, or during the wet and dry seasons. Unlike earlier studies, daily activity patterns of adult males, but not subadult males, were strongly associated with activity of females. Subadult males tended to be more active when adult males were not. Activity of Nile Bushbucks on the Mweya Peninsula generally peaked in the morning and evening, with resting periods from 08:00 h to 17:00 h and then again from 21:00 h to 24:00 h. No association of activity and sunlight intensity was noted, nor between nocturnal activity and phase of the moon.

Movements, Home range and Social organization. On the Mweya Peninsula in the 1970s, Nile Bushbucks moved 193-947 m while foraging during the day, and night time foraging movements were greater, at 1095-1233 m. More recent work there in the early 2000s showed that female densities increased with increasing canopy cover but home range sizes decreased. Such cover was related to avoidance of predators such as Lions (Panthera leo), Leopards (P. pardus), and Spotted Hyenas (Crocuta crocuta). Female densities in matrilineal clans were 6-7-19-6 ind/km?. In the same studies, female Nile Bushbucks claimed a home range in their natal area and associated most often with related females; home ranges of related females overlapped a great deal and overlapped less with those of unrelated individuals. Aggressive behavior was more frequent between unrelated females. Mature male Nile Bushbucks (more than five years old) lacked a linear dominance hierarchy among themselves; rather, they defended a home range from other males, particularly a core area that they scent-marked by rubbing oily secretions from their horn bases and cheeks. Locations of scent marking were focused on deliberate sites within a core area that was about 50% of a male’s home range. Male home ranges overlapped those of females, and the size of a male’s territory expanded when more potential mates were available. With expanding territory size, however, intrusion pressure from neighboring territory holders, also attempting to gain mates, increased. Overt aggression between mature males was rare but occurred when a territory holder was challenged. Mature males attempted to dominate subadult non-terrritorial males (3-5 year olds), but copulation rates were not different between them. Subadults were able to participate in breeding by adopting a sneaking strategy while mature males were preoccupied with scent marking and defending their territory from other mature males. Subadult males with longer horns copulated more often than those with shorter horns. Only future research will determine how many of the bushbuck species display these patterns. As with other bushbuck species, the Nile Bushbuck is seen most often alone or in mother—offspring pairs. Like some other bovids, male and female Nile Bushbucks, particularly females, repeatedly defecate and urinate at the same location. The purpose of these latrines seems to be related to intersexual communication rather than territorial marking.

Status and Conservation. Classified as Least Concern on The IUCN Red List (under T: scriptus ), which does not differentiate the eight species identified here. In the late 1990s, the number of bushbucks range-wide was estimated conservatively at over 1-34 million, and they were not particularly dependent on conservation initiatives, such as protected areas, if adequate cover and water were available. Bushbuck populations are considered stable range-wide, but in localized areas, some populations have decreased because of excessive illegal harvest, destruction of native habitats as human populations and livestock numbers have increased, and increased aridity. Generally, however, bushbucks can do well in areas of human habitation because of their secretive nature, non-herding tendencies, cryptic coat patterning and tendency to freeze and blend into their surroundings when faced with danger, and their adopting a nocturnal pattern in areas of human activity. Nile Bushbucks remain common throughout their range.

Bibliography. Ansell (1972), Apio & Wronski (2005), Apio, Plath & Wronski (2006), Apio, Plath, Tiedemann & Wronski (2007), Bro-Jorgensen (2008), East (1999), Estes (1991a, 1991b), Groves & Grubb (2011), IUCN/SSC Antelope Specialist Group (2009), Kingdon (1982, 1997), Lydekker & Blaine (1914), Moodley & Bruford (2007), Moodley et al. (2009), Nowak (1999), Okiria (1980), Olson et al. (2001), Plumptre & Harris (1995), Walther (1990a), Waser (1975a, 1975b), Wronski (2005), Wronski & Moodley (2009), Wronski & Plath (2006), Wronski, Apio & Plath (2006a, 2006b, 2009), Wronski, Apio, Baranga & Plath (2006), Wronski, Apio, Wanker & Plath (2006), Wronski, Tiedemann et al. (2006).

Figures

14. Saola (Pseudoryx nghetinhensis), 16. Chowsingha (Tetracerus quadricornis), 17. Nyala (Nyala angasii)

Distribution. E Central African Republic , extreme NE DR Congo , S Sudan , W Uganda , NW Kenya , and Rwanda . The Nile Bushbuck may range further west than illustrated here because recent genetic analyses by Y. Moodley and colleagues suggest it can occur in all of the Central African Republic and southern Chad . More research is required to clearly establish the ranges of the Nile Bushbuck and the Central Bushbuck ( T. phaleratus ).