|Mature male impala in Serengeti National Park, Tanzania|
The impala (Aepyceros melampus) is a medium-sized African antelope. It is the type species of the genus Aepyceros and belongs to the family Bovidae. It was first described by German zoologist Martin Hinrich Carl Lichtenstein in 1812. Two subspecies of the impala have been recognised: the common impala (A. m. melampus) and the black-faced impala (A. m. petersi). The impala is typically between 120–160 cm (47–63 in) in head-and-body length. Males stand up to approximately 75–92 cm (30–36 in) at the shoulder, while the height of the females is 70–85 cm (28–33 in). Males typically weigh 53–76 kg (117–168 lb) and females 40–53 kg (88–117 lb). The impala is characterised by a glossy, reddish brown coat. As a sign of sexual dimorphism, only the males have horns, which are 45–92 cm (18–36 in) long.
The black wildebeest is a mixed forager, whose diet consists of grasses, forbs, monocots, dicots and foliage. It usually switches between grazing and browsing depending on the season and habitat. Water is an essential requirement. There are three distinct social groups: the female herds, the bachelor herds and the territorial bulls. They are fast runners, and communicate using a variety of visual and vocal communication. The impala is known for its giant leaps, as high as 3 m (9.8 ft). The mating season for the impala is the three-week long period toward the end of the wet season in May. A single calf is usually born after a gestational period of about six to seven months. The calf remains with its mother for four to six months, after which it joins juvenile groups. The impala inhabits savanna grasslands and woodlands close to water sources.
The impala is native to Angola, Botswana, Kenya, Malawi, Mozambique, Namibia, Rwanda, South Africa, Swaziland, Tanzania, Uganda, Zambia and Zimbabwe. Regionally extinct in Burundi, it has been introduced in Gabon. The black-faced impala is confined to Kaokoland (Namibia) and southwestern Angola. The common impala has been widely introduced in southern Africa, and also in two protected areas of Gabon. Though there are no major threats to the survival of the impala, poaching and natural calamities have significantly contributed to the decline of the black-faced impala. While the common impala has been listed as of Least Concern by the International Union for Conservation of Nature (IUCN), the black-faced impala has been rated as Vulnerable.
Etymology and taxonomy
The scientific name of the impala is Aepyceros melampus. It is the type species of the genus Aepyceros and belongs to the family Bovidae. It was first described by German zoologist Martin Hinrich Carl Lichtenstein in 1812. The vernacular name "impala" comes from the Zulu language meaning "gazelle". The scientific name, Aepyceros melampus, is derived from Greek words αιπος aipos ("high"), κερος ceros ("horn") and melas ("black"), pous ("foot").
Pertaining to its close affinity to some species of gazelles, the kob and reedbucks, taxonomists had placed the impala in the same tribe as these alcelaphines. Its resemblance to the hartebeest led palaeontologist Elisabeth Vrba to consider the impala as a sister clade to the alcelaphines, and Aepyceros was included under subfamily Alcelaphinae in 1985. However, the impala was subsequently placed in its own tribe, Aepycerotini, in 1992, which has been elevated to subfamily status. An rRNA and β-spectrin nuclear sequence analysis supported an association between Aepyceros and Neotragus.
Up to six subspecies have been described, although only two are usually distinguished, supported by mitochondrial DNA analysis. These are the common impala (A. m. melampus) and the black-faced impala (A. m. petersi). While the former is abundant in southern and eastern Africa, the latter is restricted to southwestern Africa. Both subspecies show much genetic differentiation. No hybrids are known between these subspecies. Several fossil species are known, including A. datoadeni from the Pliocene of Ethiopia.
A study by Vrba revealed that while the common alcelaphine ancestor has diverged at least 18 times into various morphologically different forms of hartebeest and wildebeest, the impala has continued in its basic form since at least five million years. The oldest fossil discovered suggests the impala was slightly smaller than the modern form, but otherwise similar in all respects to the latter. Even the two subspecies of impala have only a few differences between them. This implies that the impala was perfectly adapted to its environment. Its gregarious nature, variety in diet, high population growth, defence against ticks and cooperation with oxpeckers who feed on ticks might have been some of the traits that prevented major changes in morphology and behaviour in the impala.
The impala is a sexually dimorphic antelope, with the males larger than the females. The head-and-body length is typically between 120–160 cm (47–63 in). Males reach approximately 75–92 cm (30–36 in) at the shoulder, while females reach 70–85 cm (28–33 in). Males typically weigh 53–76 kg (117–168 lb) and females 40–53 kg (88–117 lb). The tail is 30–45 cm (12–18 in) long. The impala is comparable in size to the kob.
The impala has a glossy, reddish brown coat. The red hue fades away towards the sides and the underside is white. The white rings around the eyes and the light chin and muzzle are distinct features. Apart from these features, there are black stripes on the rump, the tail, the forehead. The ears are also tipped with black. The impala has a strong resemblance to the gerenuk in terms of colouration. However, the gerenuk has shorter horns and lacks the black thigh stripes of the impala. The impala has scent glands covered by the black tuft of hair on the back feet. Sebaceous glands are concentrated on the forehead and dispersed on the torso of dominant males. The forehead glands present in 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. The impala has an average lifespan of about 15 years in the wild, and nearly 17 years in captivity.
As a prominent sign of sexual dimorphism, only the males possess horns which are 45–92 cm (18–36 in) long. The lyre-shaped horns resemble the letter "S", and are slender. The horns have strong ridges and the tips are far apart. They are circular in section and hollow at the base. Their arch-like structure helps the animal to interlock the horns and throw off the opponent. These also protect the cranium from damage.
The impala, like other small to medium-sized African antelope, 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 and remove ectoparasites. In allogrooming, adult males and females groom one another orally on the head and neck. There are generally six to twelve bouts of allogrooming. Allogrooming in females is generally between related individuals, whereas that occurring in males is usually between unrelated individuals. The bulbourethral glands are heavier and testosterone levels are nearly double in territorial males in comparison to bachelors.
Of the subspecies, the black-faced impala is significantly larger as well as darker than the common impala. A recessive gene causes the black coloration in these animals. The black tip on the ear is much larger in the former, and the tail is almost 30% longer and bushier than the common impala.
Ecology and behaviour
The impala are diurnal, most active shortly after dawn and before dusk. They spend the night feeding and resting. They use various kinds of visual, olfactory and auditory communication - most notably "empty-kicking", "tongue-flashing", laying scent-trails and giving loud roars - which are unique to the impala. The roaring process consists of one to three loud snorts with mouth closed, followed by two to ten deep grunts with an open mouth, lifted chin and upraised tail. The most characteristic movement of the impala is its giant leaps, over bushes and even other impala. When alarmed, the impala run at considerably high speeds and jump to heights of 3 m (9.8 ft), covering distances between 8.5 and 9 m (28 and 30 ft). Unlike other antelopes, who run away in the open when disturbed, the impala tries to hide itself in dense vegetation in case of any alarm. Carnivores like lions, leopards, Cape hunting dogs, spotted hyenas, crocodiles and pythons usually prey over the impala.
The impala form three distinct social groups in the wet season - the territorial males, bachelor herds and female herds. The impala continually break up into smaller herds and reunite, and often desert their territories. The territorial bulls may or may not have breeding females in their territories. The bull will try to control any female herds passing through his territory, and may change territories according to the season. Whenever a female herd enters his territory, the bull will herd them towards the centre, and will also chase away any bachelor males or juveniles who accompany the herd. About a third of the adult males hold territories, which range from 0.2–0.9 km2 (2,200,000–9,700,000 sq ft) in size. The males demarcate their territories with urine and faeces and defend them against any male intruders. Males in rut prefer having small, heavily defend territories and can return to their old ones to reclaim them. A study of impala in the Serengeti National Park showed that in 94% of the males, territoriality was observed only for a duration of less than four months.
The bachelor herds comprise of non-territorial adult as well as juvenile males, and can have about 30 members. They maintain an individual distances of 2.5–3 m (8.2–9.8 ft). Young and old males may interact preferentially, but middle-aged males usually avoid one another. The female herds consist of 15-100 individuals, and comprise of breeding herds of females and their young (including young males below four years). The females form clans, and inhabit home ranges 80–180 hectares (200–440 acres; 0.31–0.69 sq mi) in size. There is no distinct leader of the female herd, though animals aged five years or more may move independently. Membership in both bachelor and female is variable. The social behaviour of the impala is influenced by the seasons. While the home ranges are heavily fortified in the wet season, but clans often overlap in the dry season. While the southern impala are much likely to intermix in the dry season, the eastern impala prefer being territorial during this period.
The impala is an adaptable forager, due to which it need not migrate long distances as other antelopes have to. The impala has a regular requirement of water, and generally inhabits places with water sources nearby; though it can survive on green succulent vegetation in case water is scarce. Upper incisors and canines are absent in these ruminants, and the cheek teeth are folded and sharp. Impalas usually feed in herds after dawn, before dusk and in the night. They stop feeding if it rains, and face away from the wind. The animals assemble nearer to one another (females bunch closer), and begin ruminating. The animals who feed on the periphery of the herds are usually more vigilant against predation risk than those feeding in the centre of the herds. A foraging impala will try to defend the patch it is feeding on by lowering its head. A study revealed that time spent by the impala in foraging is maximum (75.5%) in the late dry season, decreases through the rainy season, and is minimum in the early dry season (57.8%).
Unlike its relatives, the impala has a variable diet. It usually switches between grazing and browsing depending on the season and habitat. As it can utilize both monocots and dicots, and feed on fruits and Acacia pods wherever available, the impala can have an adequate and nutritious diet. An analysis showed that the diet of impala consists of 45% monocots, 45% dicots and 10% fruits. Proportion of grasses in the diet increases remarkably after the first rains (up to 90% of the diet consists of grasses), but declines in the dry season. In the late wet and dry season, forbs are the main item of the diet. Diets are nutritionally poor in the mid-dry season, when impala feed mostly on woody dicots. Another study revealed that dicot proportion in the diet of territorial males is minimum, while t is much higher in bachelors and females.
Though males are sexually mature by the time they are a year old, they actually mate only after the age of four years, when they establish their own territories. Females conceive after they are a year and a half old. The annual three-week long breeding season of the impala, also called the rut, begins toward the end of the wet season in May; but the males begin preparations for mating since March. The shorter duration of the days in March leads to increased gonadal growth and hormone production in the males, resulting in greater aggressiveness and territoriality in them. Males undergo several physical changes as well - such as darkening of the coat due to greasy secretions from the sebaceous glands, thickening of the neck and acquiring a musky odour. The rut is also influenced by the lunar cycle, with most mating taking place between full moons.
Rutting males fight over dominance, often giving out noisy roars and chasing on another. They walk stiffly and display their neck and horns. Territorial males usually reduce feeding and allogrooming during the mating season, probably in order to devote more time on the outlook for females in estrous. The male detects estrous in the female by testing her urine. The estrous cycle is 12 to 29 days and lasts for 24 to 48 hours. On coming across a breeding female, the excited male begins the courtship by chasing the female about. This gradually turns into a walk, with the female 3–5 m (9.8–16.4 ft) ahead of her mate. The male now flicks his tongue and may nod vigorously. Then the female allows him to lick her vulva, and holds her tail to a side. The male tries mounting the female, holding his head high and clasping her with his forelegs. Mounting attempts may be repeated every few seconds to every minute or two. The male usually loses interest in the female after the first copulation, though she is still active and can mate with other males. The male is no more territorial now, and may join the bachelor herds.
The gestational period is of six to seven months, after which a single calf is born. However, the mother has the ability to delay giving birth for an additional month if conditions are harsh. When giving birth (usually in the midday), the female will isolate herself from the herd, despite numerous attempts by the male to keep her in his territory. The female will keep the fawn in an isolated spot for a few days or even leave it lying out in hiding for a few days, weeks, or more, before returning to the herd. There, the fawn will join a nursery group and will go to its mother only to nurse or when predators are near. Fawns are suckled for four to six months. Males which mature are forced out of the group and will join bachelor herds.
Distribution and habitat
The impala, a typical ecotone species, inhabits savanna grasslands and woodlands close to water sources. They show a preference for acacia savannas for their nutritious grasses and browse in the dry season. While they inhabit Acacia senegal woodlands in the wet season, they prefer A. drepanolobium savannas in the dry season. Impala in southern Africa have been found to be associated with Colophospermum mopane woodlands. High population densities are observed in places with short grasses. They may also choose habitats with shade, as they are not adapted to dry heat. Black-faced impala, who live in semi-arid environments, also select the interface between wooded savannas and open grassy wetlands. Impala are not known to be part of montane ecosystems.
A study found that the reduction of woodland cover and creation of shrublands by the African bush elephants has favoured impala population by increasing the availability of more dry season browse. Earlier, the Baikiaea woodland, that has now declined due to elephants, provided minimum browse to impala. The newly formed Capparis shrubland, on the other hand, can be a key browsing habitat.
The impala is native to Angola, Botswana, Kenya, Malawi, Mozambique, Namibia, Rwanda, South Africa, Swaziland, Tanzania, Uganda, Zambia and Zimbabwe. Regionally extinct in Burundi, it has been introduced in Gabon. The current distribution of the impala is not much different from its historical range. The black-faced impala is confined to Kaokoland (Namibia) and southwestern Angola. The common impala has been widely introduced in southern Africa, and also in two protected areas of Gabon.
Threats and conservation
Though there are no major threats to the survival of the impala, poaching and natural calamities have significantly contributed to the decline of the black-faced impala. Where the black-faced impala lives alongside the common impala, there is a risk of hybridisation between the two subspecies, and this is regarded as a potential threat to the maintenance of the species. Translocation of the black-faced impala can be highly beneficial in conserving the populations, especially when larger populations are introduced into a place at first.
The population of the common impala has been estimated to be around 2 million, while that of the black-faced impala is only 2,000-3,000. While the common impala has been listed as of Least Concern by the International Union for Conservation of Nature (IUCN), the black-faced impala has been rated as Vulnerable. The common impala is one of the most abundant antelopes in Africa, with about one-quarter of the population occurring in protected areas. The largest populations occur in the Masai Mara and Kajiado (Kenya); the Serengeti, Ruaha National Parks and Selous Game Reserve (Tanzania); Luangwa Valley (Zambia); Okavango Delta (Botswana); Hwange, Sebungwe and Zambezi Valley (Zimbabwe); and Kruger National Park (South Africa). The rare black-faced impala has been reintroduced from Kaokoland into private farms in Namibia and the Etosha National Park. The Namibian government has a management plan to avoid hybridisation between the black-faced impala and the common impala. Population densities vary largely from place to place; from less than 1/km² in Mkomazi National Park (Tanzania) to as high as 135/km² near Lake Kariba (Zimbabwe).
- IUCN SSC Antelope Specialist Group (2008). Aepyceros melampus. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 18 January 2009. Database entry includes a brief justification of why this species is of least concern
- Grubb, P. (2005). "Order Artiodactyla". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. p. 673. ISBN 978-0-8018-8221-0. OCLC 62265494.
- Huffman, B. "Impala". Ultimate Ungulate. Retrieved 14 October 2012.
- Kingdon, J.; Butynski, T.; Happold, D. (2013). Mammals of Africa. London: Bloomsbury Publishing. pp. 479–84. ISBN 1408189968.
- Estes, R. D. (2004). The Behavior Guide to African Mammals : Including Hoofed Mammals, Carnivores, Primates (4th ed.). Berkeley: University of California Press. pp. 158–66. ISBN 0520080858.
- Groves, C.; Grubb, P. (2011). Ungulate Taxonomy. Baltimore, Maryland: Johns Hopkins University Press. ISBN 1-4214-0093-6.
- Kuznetsova, M. V.; Kholodova, M. V. (2003). "Revision of phylogenetic relationships in the Antilopinae subfamily on the basis of the mitochondrial rRNA and β-spectrin nuclear gene sequences". Doklady Biological Sciences 391 (1-6): 333–6. doi:10.1023/A:1025102617714. ISSN 1608-3105.
- Nersting, L. G.; Arctander, P. (2001). "Phylogeography and conservation of impala and greater kudu". Molecular Ecology 10 (3): 711–719. doi:10.1046/j.1365-294x.2001.01205.x.
- Lorenzen, E. D.; Arctander, P.; Siegismund, H. R. (11 January 2006). "Regional genetic structuring and evolutionary history of the impala (Aepyceros melampus)". Journal of Heredity 97 (2): 119–32. doi:10.1093/jhered/esj012.
- Lorenzen, E. D.; Siegismund, H. R. (14 October 2004). "No suggestion of hybridization between the vulnerable black-faced impala (Aepyceros melampus petersi) and the common impala (A. m. melampus) in Etosha National Park, Namibia". Molecular Ecology 13 (10): 3007–19. doi:10.1111/j.1365-294X.2004.02308.x.
- Geraads, D., et al. (2012). "Pliocene Bovidae (Mammalia) from the Hadar Formation of Hadar and Ledi-Geraru, Lower Awash, Ethiopia". Journal of Vertebrate Paleontology 32 (1): 180–197. doi:10.1080/02724634.2012.632046.
- Lundrigan, B.; Sproull, K. "Aepyceros melampus (Impala)". University of Michigan Museum of Zoology. Animal Diversity Web. Retrieved 14 October 2012.
- Armstrong, M. (2007). Wildlife and Plants (3rd ed.). New York: Marshall Cavendish. p. 538-9. ISBN 978-0-7614-7693-1.
- Welsch, U.; van Dyk, G.; Moss, D.; Feuerhake, F. (23 April 1998). "Cutaneous glands of male and female impalas ( Aepyceros melampus ): seasonal activity changes and secretory mechanisms". Cell and Tissue Research 292 (2): 377–94. doi:10.1007/s004410051068. ISSN 1432-0878.
- "Impala (Aepyceros melampus)". Wildscreen. ARKive. Retrieved 27 February 2014.
- McKenzie, A. A. (June 1990). "The ruminant dental grooming apparatus". Zoological Journal of the Linnean Society 99 (2): 117–28. doi:10.1111/j.1096-3642.1990.tb00564.x.
- Hart, B. L.; Hart, L. A. (1992). "Reciprocal allogrooming in impala, Aepyceros melampus". Animal Behaviour 44 (6): 1073–83. doi:10.1016/S0003-3472(05)80319-7.
- Bramley, P. S.; Neaves, W. B. (1972). "The relationship between social status and reproductive activity in male impala, Aepyceros melampus". Journal of Reproduction and Fertility 31 (1): 77–81. PMID 5078117.
- Carnaby, T. (2006). Beat About the Bush : mammals. Johannesburg: Jacana. p. 39. ISBN 978-1-77009-240-2.
- Nowak, R. M. (1999). Walker's Mammals of the World (6th ed.). Baltimore, Maryland: Johns Hopkins University Press. pp. 1194–6. ISBN 0801857899.
- Schenkel, R. (1966). "On sociology and behaviour in impala (Aepyceros melampus) Lichtenstein". African Journal of Ecology 4 (1): 99–114. doi:10.1111/j.1365-2028.1966.tb00887.x.
- Murray, M. G. (August 1981). "Structure of association in impala, Aepyceros melampus". Behavioral Ecology and Sociobiology 9 (1): 23–33. doi:10.1007/BF00299849. ISSN 1432-0762.
- Blanchard, P.; Sabatier, R.; Fritz, H. (5 July 2008). "Within-group spatial position and vigilance: a role also for competition? The case of impalas (Aepyceros melampus) with a controlled food supply". Behavioral Ecology and Sociobiology 62 (12): 1863–8. doi:10.1007/s00265-008-0615-3.
- Wronski, T. (September 2002). "Feeding ecology and foraging behaviour of impala Aepyceros melampus in Lake Mburo National Park, Uganda". African Journal of Ecology 40 (3): 205–11. doi:10.1046/j.1365-2028.2002.00348.x.
- Meissner, H. H.; Pieterse, E.;Potgieter, J. H. J. (1996). "Seasonal food selection and intake by male impala Aepyceros melampus in two habitats". South African Journal of Wildlife Research 26 (2): 56–63. ISSN 0379-4369.
- Dunham, K. M. (20 August 2009). "The diet of Impala (Aepyceros melampus) in the Sengwa Wildlife Research Area, Rhodesia". Journal of Zoology 192 (1): 41–57. doi:10.1111/j.1469-7998.1980.tb04218.x.
- van Rooyen, A. F.; Skinner, J. D. (January 1989). "Dietary differences between the sexes in impala". Transactions of the Royal Society of South Africa 47 (2): 181–5. doi:10.1080/00359198909520161.
- Mooring, M. S.; Hart, B. L. (1995). "Differential grooming rate and tick load of territorial male and female impala". Behavioral Ecology 6 (1): 94–101. doi:10.1093/beheco/6.1.94.
- Jarman, M. V. (1979). Impala Social Behaviour : Territory, Hierarchy, Mating, and the Use of Space. Berlin: Parey. pp. 1–92. ISBN 3489609360.
- Sinclair, A. R. E.; Norton-Griffths, M. (1984). Serengeti, Dynamics of an Ecosystem. Chicago: University of Chicago Press. pp. 135–7. ISBN 0226760294.
- Rutina, L. P.; Moe, S. R.; Swenson, J. E. (September 2005). "Elephant Loxodonta africana driven woodland conversion to shrubland improves dry-season browse availability for impalas Aepyceros melampus". Wildlife Biology 11 (3): 207–13. doi:10.2981/0909-6396(2005)11[207:ELADWC]2.0.CO;2.
- Green, W. C. H.; Rothstein, A. (2008). "Translocation, hybridization, and the endangered black-faced impala". Conservation Biology 12 (2): 475–80. doi:10.1111/j.1523-1739.1998.96424.x.
- Matson, T.; Goldizen, A. W.; Jarman, P. J. (April 2004). "Factors affecting the success of translocations of the black-faced impala in Namibia". Biological Conservation 116 (3): 359–65. doi:10.1016/S0006-3207(03)00229-5.
|Wikispecies has information related to: Aepyceros melampus|
|Wikimedia Commons has media related to Aepyceros melampus.|