Kobus thomasi (Sclater, 1896)
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publication ID |
https://doi.org/ 10.5281/zenodo.6512484 |
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DOI |
https://doi.org/10.5281/zenodo.6636826 |
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persistent identifier |
https://treatment.plazi.org/id/03F50713-9977-FFCD-0647-F99EF9B5F79E |
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Conny |
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scientific name |
Kobus thomasi |
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Uganda Kob
French: Cobe de Thomas / German: Uganda-Grasantilope / Spanish: Kob de Uganda
Other common names: Thomas's Kob
Taxonomy. Cobus thomas: Sclater, 1896 ,
Berkeley Bay, Victoria Nyanza.
The Uganda Kob was formerly classified as a subspecies of K. kob but is considered a unique species here. Monotypic.
Distribution. Far E DR Congo, W Uganda, and S Sudan. The divisions between the ranges of the Uganda Kob, the Whiteeared Kob ( K. leucotis ), and the Loder’s Kob ( K. loderi ) in Sudan are poorly understood. View Figure
Descriptive notes. Head-body c.160-180 cm, tail c¢.10-15 cm, shoulder height c.82-100 cm; weight 94 kg (85-121 kg) in males and 63 kg (60-77 kg) in females. The Uganda Kob is the largest of the four kob species, particularly in weight and shoulder height. Mature males are approximately 50% larger than females, and have distinctly muscular necks. The smooth pelage is reddish-brown, often with golden tones, and the belly and inside upper portions of the legs are white. Distinct black markings are present on the fronts of the legs. The tail is relatively narrow; the dorsal surface is reddish with a blackish tip, and the underside is white. The head is colored similarly to the body, although the center of the face tends to be slightly darker or more richly toned. A well-defined arc of white is present at the medial corner of each eye, becoming narrower and more buff in color as it circles the eye dorsally; these markings are much larger than those seen in the neighboring Loder’s Kob . The lips and underside of the jaw are white; a white bib is situated on the upper throat and is particularly well defined in adult males. The ears of females are tawny; as males age, their ears pale to white except at the tips. Only males have horns, which are lyre-sshaped and form a distinctive sigmoid shape when viewed in profile (sweeping backward at the base and upward at the tips). The horns are stout and have prominent transverse ridges between the two principal curves; the tips are smooth. The horn bases of mature males have only thin ridges. Typical horn length is 50-61. 6 cm. Dental formula is 1 0/3, C 0/1, P3/3,M3/302)=32.
Habitat. Open grasslands interspersed with low-density Acacia woodland. The Uganda Kob is most frequently found in short-grass communities dominated by Bothriochloa, Chrysochloa, Sporobolus, or mixed Hyparrhenia and Themeda. Females in particular alter ranging patterns to maximize their use of short green grass, especially in the dry season. Areas of tall grass and swampy regions are avoided. The Uganda Kob is able to sustain high population densities in suitable habitat. Localized density of 182 ind/km? has been recorded in Queen Elizabeth National Park, Uganda, although densities average 13 ind/km? across the park. Regional densities of 20-50 ind/km? occur in Rwenzori Mountains National Park, Uganda, although the park-wide density is 8:6 ind/km?. Patches of high and low population density occur within apparently suitable habitat for undetermined reasons.
Food and Feeding. The Uganda Kob is a selective grazer, preferentially foraging on short green grasses. Based on stomach content analyses, the grasses Chloris gayana, Heteropogon contortus, Hyparrhenia filipendula, Sporobolus pyramidalis, and Themeda triandra are heavily used (all present in at least 70% of 72 stomach samples); Bothriochloa sp., Brachiaria platynota, Cynodon dactylon, and Hyparrhenia dissoluta are eaten with less frequency. Cenchrus ciliaris, Panicum repens , and Sporobolus consimilis are also consumed. Diet selection between grass species varies slightly between wet and dry seasons, and during dry seasons, shrubs such as Sida sp. and Capparis sp. are browsed with greater frequency.
Breeding. Aseasonal; calves are regularly observed throughout the year. The unusual lek system of breeding in the Uganda Kob has been well studied. Within an arena of small, densely packed male territories, estrous females exercise mate choice; the majority of copulations occur on just a few lek territories (breeding is rare outside of the lek). Female preference is for the territory itself and only indirectly for the male guarding it; selection is governed by olfactory clues (likely from urine of previous estrous females). Males holding such territories must be large and well conditioned to successfully compete for the increased access to mates. Leks are used year-round, although there is constant turnover of males. Leks are populated by the highest number of males during the late wet seasons (April-June and October-December) when plentiful forage reduces the energetic costs associated with such confined territories. A similar wet-season increase of female lek use occurs, although the number of estrous females shows much less seasonality. Males use a prancing display to attract the attention of estrous females, flashing their leg markings and throat bib. During courtship, a male will approach and smell the female, typically inciting her to urinate; the male uses the flehmen response to determine receptivity. Courting proceeds with ritualized “laufschlag,” the gentle tapping of the female’s underside with one of the male’s forelegs. Mounting may occur up to 20 times before copulation is successfully achieved, and a single female may breed with several males (as many as nine recorded) during a visit to the lek. The gestation period is an estimated 240-266 days. The single infant lies concealed in dense grass or thicket for 6-8 weeks, being visited periodically for nursing. After two months, the youngster emerges and begins to regularly follow its mother. Weaning occurs around six months of age. Young females may begin breeding as early as 13 months; post-parturient females may breed shortly after giving birth and females are thus frequently pregnant. The horns of young males begin to emerge at five months; sexual maturity may be reached after one year, but males are not able to hold a territory until after three years of age. Male life span in the wild is estimated at eight years; females likely live to around ten years, although in captivity they may survive until 18 years of age.
Activity patterns. Diurnal activity of Uganda Kobs has been well established, but nocturnal behavior remains largely unknown. Days are spent on feeding grounds; as night falls, herds travel to different areas. Females generally travel 2-5 km/day while foraging, although if they are attending to a young infant this may be substantially less. Such movements are rarely straight-line distances; the meandering pattern results in an average displacement of 1 km between morning and evening.
Movements, Home range and Social organization. The social system of the Uganda Kob is loose, and long-term associations between individuals are rare. Herds are often temporary aggregations; a single individual may be found in dramatically different sized herds over the course of 24 hours. Mixed groups of 30-50 Uganda Kobs are common, and usually have a much greater proportion ofadult females than adult males. In areas of high population density, average herd size may be as high as 185, with a range from less than 20 up to 600-1000 individuals. The largest herds are most frequent during the wet season, when this species congregates on short-grass pastures. After grass fires burn through tall-grass habitats, large Uganda Kob aggregations disperse to feed on young shoots. At low population densities, group sizes are much smaller; solitary individuals and pairs are frequent, and small bachelor herds and mixed sex groups with 5-7 animals (occasionally up to 30) are also seen. Regardless of population density, females occupy large overlapping home ranges. The average home ranges of radio-collared females are 15-20 km?, with core area of approximately 3 km?*. Home ranges of males are much smaller, 2-5 km?®, with a core range of only 0-05 km*. Approximately half of Uganda Kob males are territorial at any given time. Two-thirds of these males hold large, dispersed territories 0-2-4 km?* in size, often with a central area of very closely cropped grass. The remaining third maintain very small territories within a lek. A single lek may contain 5-65 territorial males, although 10-20 is typical; each territory is only 15-35 m in diameter, and total lek area is 0-03-0-12 km*. Lek site fidelity may last for decades. Vocal and visual advertisements, such as whistling calls and strutting with head high and ears lowered, signify the occupancy of a territory and help delineate boundaries. Neighboring males may briefly clash horns to maintain mutual borders. Serious fights occur whenever other males try to displace a territory holder; such fights are frequent in central territories that are highly attractive to females. Turnover in occupancy may occur within a few hours, although some males maintain their status for several weeks. The extreme energetic cost of defending a territory that contains very few resources is responsible for such a high rate of replacement. Lek males spend considerable time defending theirterritory (8% of daily activity compared to 1% on single territories); increased patrolling and sexual behavior further reduce the time available to feed or rest. Territories tend to enlarge at the periphery of a lek, gradually increasing to the size of single territories. Lek males may occupy single territories when not on a lek, or they may join subadult and nonterritorial males in a bachelor herd. Regardless of territory size or location, females move freely across territorial boundaries. Both males and females show lek-fidelity, usually visiting the same lek year after year.
Status and Conservation. Classified as Least Concern on The IUCN Red List (as K. kob thomasi, and including some eastern populations of K. loderi). The distribution of the Uganda Kob has been significantly reduced due to agricultural development, widespread cattle grazing, and diseases such as rinderpest. The Uganda Kob was extirpated from SW Kenya in the 1960s; populations in Tanzania (around Lake Victoria) have also been eliminated. Provided with adequate protection, however, the Uganda Kob has proven to be extremely resilient. The present population trend is stable or slightly increasing; current total numbers are estimated to be 40,000 -100,000 individuals. This species is most common in Murchison Falls National Park, Queen Elizabeth National Park (where numbers have increased dramatically in recent decades), and the Toro-Semliki area of Uganda.
Bibliography. Balmford (1992), Balmford et al. (1992), Buechner (1961), Deutsch (1994), Deutsch & Nefdt (1992), Deutsch & Ofezu (1994), East (1999), Field (1968, 1972), IUCN/SSC Antelope Specialist Group (2008aa), Kingdon (1982), Leuthold (1966), Lydekker (1914), Modha & Eltringham (1976), Stubblefield (1995), Weigl (2005).
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