Impala
The impala or rooibok is a medium-sized antelope found in eastern and southern Africa. The only extant member of the genus Aepyceros, and tribe Aepycerotini, it was first described to Europeans by German zoologist Hinrich Lichtenstein in 1812. Two subspecies are recognised—the grassland-dwelling common impala, and the larger and darker black-faced impala, which lives in slightly more arid, scrubland environments. The impala reaches at the shoulder and weighs. It features a glossy, reddish brown coat. The male's slender, lyre-shaped horns are long.
Active mainly during the day, the impala may be gregarious or territorial depending upon the climate and geography. Three distinct social groups can be observed: the territorial males, bachelor herds and female herds. The impala is known for two characteristic leaps that constitute an anti-predator strategy. Browsers as well as grazers, impala feed on monocots, dicots, forbs, fruits and acacia pods. An annual, three-week-long rut takes place toward the end of the wet season, typically in May. Rutting males fight over dominance, and the victorious male courts females in oestrus. Gestation lasts six to seven months, following which a single calf is born and immediately concealed in cover. Calves are suckled for four to six months; young males—forced out of the all-female groups—join bachelor herds, while females may stay back.
The impala is found in woodlands and sometimes on the interface between woodlands and savannahs; it inhabits places near water. While the black-faced impala is confined to southwestern Angola and Kaokoland in northwestern Namibia, the common impala is widespread across its range and has been reintroduced in Gabon and southern Africa. The International Union for Conservation of Nature classifies the impala as a species of least concern; the black-faced subspecies has been classified as a vulnerable species, with fewer than 1,000 individuals remaining in the wild as of 2008.
Etymology
The first attested English name, in 1802, was palla or pallah, from the Tswana phala 'red antelope'; the name impala, also spelled impalla or mpala, is first attested in 1875, and is directly from Zulu. Its Afrikaans name, rooibok 'red buck', is also sometimes used in English.The scientific generic name Aepyceros comes from Ancient Greek + κέρας ; the specific name melampus from μελάς + πούς.
Taxonomy and evolution
The impala is the sole member of the genus Aepyceros and belongs to the family Bovidae. It was first described by German zoologist Martin Hinrich Carl Lichtenstein in 1812. In 1984, palaeontologist Elisabeth Vrba opined that the impala is a sister taxon to the alcelaphines, given its resemblance to the hartebeest. A 1999 phylogenetic study by Alexandre Hassanin and colleagues, based on mitochondrial and nuclear analyses, showed that the impala forms a clade with the suni. This clade is sister to another formed by the bay duiker and the klipspringer. An rRNA and β-spectrin nuclear sequence analysis in 2003 also supported an association between Aepyceros and Neotragus. The following cladogram is based on the 1999 study:Up to six subspecies have been described, although only two are generally recognised on the basis of mitochondrial data. Though morphologically similar, the subspecies show a significant genetic distance between them, and no hybrids between them have been reported.
- A. m. melampus Lichtenstein, 1812: Known as the common impala, it occurs across eastern and southern Africa. The range extends from central Kenya to South Africa and westward into southeastern Angola.
- A. m. petersi Bocage, 1879: Known as the black-faced impala, it is restricted to southwestern Africa, occurring in northwestern Namibia and southwestern Angola.
Description
The impala is a medium-sized, slender-bodied antelope, comparable to the kob, puku and Grant's gazelle in size and build. The head-and-body length is around. Males reach approximately at the shoulder, while females are tall. Males typically weigh and females. Sexually dimorphic, females are hornless and smaller than males. Males grow slender, lyre-shaped horns long. The horns, strongly ridged and divergent, are circular in section and hollow at the base. Their arch-like structure allows interlocking of horns, which helps a male throw off his opponent during fights; horns also protect the skull from damage.The glossy coat of the impala shows two-tone colourationthe reddish brown back and the tan flanks; these are in sharp contrast to the white underbelly. Facial features include white rings around the eyes and a light chin and snout. The ears, long, are tipped with black. Black streaks run from the buttocks to the upper hindlegs. The bushy white tail, long, features a solid black stripe along the midline. The impala's colouration bears a strong resemblance to the gerenuk, which has shorter horns and lacks the black thigh stripes of the impala. The impala has scent glands covered by a black tuft of hair on the hindlegs. 2-Methylbutanoic Acid and 2-Nonanone have been identified from this gland. Sebaceous glands concentrated on the forehead and dispersed on the torso of dominant males are most active during the mating season, while those of females are only partially developed and do not undergo seasonal changes. There are four nipples.
Of the subspecies, the black-faced impala is significantly larger and darker than the common impala; melanism is responsible for the black colouration. Distinctive of the black-faced impala is a dark stripe, on either side of the nose, that runs upward to the eyes and thins as it reaches the forehead. Other differences include the larger black tip on the ear, and a bushier and nearly 30% longer tail in the black-faced impala.
The impala has a special dental arrangement on the front lower jaw similar to the toothcomb seen in strepsirrhine primates, which is used during allogrooming to comb the fur on the head and the neck and remove ectoparasites.
Ecology and behaviour
The impala is diurnal, though activity tends to cease during the hot midday hours; they feed and rest at night. Three distinct social groups can be observedthe territorial males, bachelor herds and female herds. The territorial males hold territories where they may form harems of females; territories are demarcated with urine and faeces and defended against juvenile or male intruders. Bachelor herds tend to be small, with less than 30 members. Individuals maintain distances of from one another; while young and old males may interact, middle-aged males generally avoid one another except to spar. Female herds vary in size from 6 to 100; herds occupy home ranges of. The mother–calf bond is weak, and breaks soon after weaning; juveniles leave the herds of their mothers to join other herds. Female herds tend to be loose and have no obvious leadership. Allogrooming is an important means of social interaction in bachelor and female herds; in fact, the impala appears to be the only ungulate to display self-grooming as well as allogrooming. In allogrooming, females typically groom related impalas, while males associate with unrelated ones. Each partner grooms the other six to twelve times.Social behaviour is influenced by the climate and geography; as such, the impala are territorial at certain times of the year and gregarious at other times, and the length of these periods can vary broadly among populations. For instance, populations in southern Africa display territorial behaviour only during the few months of the rut, whereas in eastern African populations, territoriality is relatively minimal despite a protracted mating season. Moreover, territorial males often tolerate bachelors, and may even alternate between bachelorhood and territoriality at different times of the year. A study of impala in the Serengeti National Park showed that in 94% of the males, territoriality was observed for less than four months.
The impala is an important prey species for Africa's large carnivores, such as cheetahs, leopards, wild dogs, lions, hyenas, crocodiles and pythons. The antelope displays two characteristic leapsit can jump up to, over vegetation and even other impala, covering distances of up to ; the other type of leap involves a series of jumps in which the animal lands on its forelegs, moves its hindlegs mid-air in a kicking fashion, lands on all fours and then rebounds. It leaps in either manner in different directions, probably to confuse predators. At times, the impala may also conceal itself in vegetation to escape the eye of the predator. The most prominent vocalisation is the loud roar, delivered through one to three loud snorts with the mouth closed, followed by two to ten deep grunts with the mouth open and the chin and tail raised; a typical roar can be heard up to away. Scent gland secretions identify a territorial male. Impalas are sedentary; adult and middle-aged males, in particular, can hold their territories for years.