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Impala

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For other uses, seeImpala (disambiguation).

Impala
Impala (Aepyceros melampus) male Kruger.jpg
male
female with calf
both inKruger National Park,South Africa
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Family: Bovidae
Tribe: Aepycerotini
Genus: Aepyceros
Species:
A. melampus
Binomial name
Aepyceros melampus
Subspecies
  • A. m. melampusLichtenstein, 1812
  • A. m. petersiBocage,1879
Distribution:
Black-faced impala
Common impala
Synonyms[2]
List
  • A. holubiLorenz, 1894
  • A. johnstoniThomas,1893
  • A. katangaeLönnberg,1914
  • A. pallah(Gervais,1841)
  • A. rendilisLönnberg, 1912
  • A. typicusThomas, 1893

Theimpalaorrooibok(Aepyceros melampus) is a medium-sizedantelopefound ineasternandsouthern Africa.Theonlyextantmember of thegenusAepyceros,and tribeAepycerotini,it was firstdescribedto Europeans by German zoologistHinrich Lichtensteinin 1812. Twosubspeciesare recognised—the grassland-dwellingcommon impala(sometimes referred to as theKenyan impala), and the larger and darkerblack-faced impala,which lives in slightly more arid, scrubland environments. The impala reaches 70–92 cm (28–36 in) at the shoulder and weighs 40–76 kg (88–168 lb). It features a glossy, reddish browncoat.The male's slender,lyre-shapedhornsare 45–92 cm (18–36 in) long.

Active mainlyduring the day,the impala may begregariousorterritorialdepending 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-predatorstrategy.Browsersas well as grazers, impala feed onmonocots,dicots,forbs,fruitsandacaciapods (whenever available). An annual, three-week-longruttakes place toward the end of the wet season, typically in May. Rutting males fight overdominance,and the victorious male courts females inoestrus.Gestationlasts six to seven months, following which a single calf is born and immediately concealed in cover. Calves aresuckledfor 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 (ecotone) between woodlands andsavannahs;it inhabits places near water. While the black-faced impala is confined to southwesternAngolaandKaokolandin northwesternNamibia,the common impala is widespread across its range and has been reintroduced inGabonand southern Africa. TheInternational Union for Conservation of Nature(IUCN) classifies the impala as aspecies of least concern;the black-faced subspecies has been classified as avulnerable species,with fewer than 1,000 individuals remaining in the wild as of 2008.

Etymology[edit]

The first attested English name, in 1802, was palla or pallah, from theTswanaphala'red antelope';[3]the nameimpala,also spelledimpallaormpala,is first attested in 1875, and is directly fromZulu.[4]ItsAfrikaansname,rooibok'red buck', is also sometimes used in English.[5]

Thescientificgeneric nameAepyceros(lit.‘high-horned’) comes fromAncient Greekαἰπύς(aipus,'high, steep') +κέρας(keras,'horn');[6][7]thespecific namemelampus(lit.‘black-foot’) fromμελάς(melas,'black') +πούς(pous,'foot').[8]

Taxonomy and evolution[edit]

See also:List of bovids

The impala is thesole memberof the genusAepycerosand belongs to thefamilyBovidae.It was firstdescribedby German zoologistMartin Hinrich Carl Lichtensteinin 1812.[2]In 1984, palaeontologistElisabeth Vrbaopined that the impala is asister taxonto thealcelaphines,given its resemblance to thehartebeest.[9]A 1999phylogeneticstudy by Alexandre Hassanin (of theNational Centre for Scientific Research, Paris) and colleagues, based onmitochondrialandnuclearanalyses, showed that the impala forms acladewith thesuni(Neotragus moschatus). This clade is sister to another formed by thebay duiker(Cephalophus dorsalis) and theklipspringer(Oreotragus oreotragus).[10]AnrRNAandβ-spectrinnuclear sequence analysis in 2003 also supported an association betweenAepycerosandNeotragus.[11]The following cladogram is based on the 1999 study:[10]

Sheep(Ovis aries)

Bontebok(Damaliscus pygargus)

Sable antelope(Hippotragus niger)

Klipspringer(Oreotragus oreotragus)

Bay duiker(Cephalophus dorsalis)

Impala(Aepyceros melampus)

Suni(Neotragus moschatus)

Grant's gazelle(Nanger granti)

Mountain reedbuck(Redunca fulvorufula)

Up to sixsubspecieshave been described, although only two are generally recognised on the basis of mitochondrial data.[12]Though morphologically similar,[13]the subspecies show a significantgenetic distancebetween them, and nohybridsbetween them have been reported.[13][14]

  • A. m. melampusLichtenstein, 1812:Known as the common impala, it occurs across eastern and southern Africa. The range extends from centralKenyatoSouth Africaand westward into southeasternAngola.
  • A. m. petersiBocage,1879:Known as the black-faced impala, it is restricted to southwestern Africa, occurring in northwesternNamibiaand southwestern Angola.

According to Vrba, the impala evolved from an alcelaphine ancestor. She noted that while this ancestor hasdivergedat least 18 times into various morphologically different forms, the impala has continued in its basic form for at least five million years.[9][15]Severalfossilspecies have been discovered, includingA. datoadenifrom thePlioceneofEthiopia.[16]The oldest fossil discovered suggests its ancient ancestors were slightly smaller than the modern form, but otherwise very similar in all aspects to the latter. This implies that the impala has efficiently adapted to its environment since prehistoric times. Its gregarious nature, variety in diet, positive population trend, defence againstticksandsymbioticrelationship with the tick-feedingoxpeckerscould have played a role in preventing major changes in morphology and behaviour.[9]

Description[edit]

A grooming male at Serengeti National Park
Close view of a male, with characteristic lyre-shaped horns, white tail and several black markings

The impala is a medium-sized, slender-bodiedantelope,comparable to thekob,pukuandGrant's gazellein size and build.[17]The head-and-body length is around 130 centimetres (51 in).[18]Males reach approximately 75–92 cm (30–36 in) at the shoulder, while females are 70–85 cm (28–33 in) tall. Males typically weigh 53–76 kilograms (117–168 lb) and females 40–53 kg (88–117 lb).Sexually dimorphic,females are hornless and smaller than males. Males grow slender, lyre-shaped horns 45–92 cm (18–36 in) long.[17]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.[13][17]

The glossy coat of the impala shows two-tone colouration – the 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 andsnout.The ears, 17 cm (6.7 in) long, are tipped with black.[13][19]Black streaks run from the buttocks to the upper hindlegs. The bushy white tail, 30 cm (12 in) long, features a solid black stripe along the midline.[19]The impala's colouration bears a strong resemblance to thegerenuk,which has shorter horns and lacks the black thigh stripes of the impala.[13]The impala hasscent glandscovered by a black tuft of hair on the hindlegs. 2-Methylbutanoic Acid and 2-Nonanone have been identified from this gland.[20]Sebaceous glandsconcentrated on the forehead and dispersed on the torso of dominant males[17][21]are most active during the mating season, while those of females are only partially developed and do not undergo seasonal changes.[22]There are fournipples.[17]

Of the subspecies, the black-faced impala is significantly larger and darker than the common impala;melanismis responsible for the black colouration.[23]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.[18][19]Other differences include the larger black tip on the ear, and a bushier and nearly 30% longer tail in the black-faced impala.[13]

The impala has a special dental arrangement on the front lower jaw similar to thetoothcombseen instrepsirrhine primates,[24]which is used duringallogroomingto comb the fur on the head and the neck and removeectoparasites.[13][25]

Ecology and behaviour[edit]

An impala mid-air during a leap
Impala can leap up to 3 m (9.8 ft).

The impala isdiurnal(active mainly during the day), though activity tends to cease during the hot midday hours; they feed and rest at night.[17]Three distinct social groups can be observed – theterritorialmales, bachelor herds and female herds.[26]The territorial males hold territories where they may formharemsof females; territories are demarcated with urine and faeces and defended against juvenile or male intruders.[17]Bachelor herds tend to be small, with less than 30 members. Individuals maintain distances of 2.5–3 m (8.2–9.8 ft) 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 occupyhome rangesof 80–180 ha (200–440 acres; 0.31–0.69 sq mi). 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.[17][27]Allogrooming is an important means of social interaction in bachelor and female herds; in fact, the impala appears to be the onlyungulateto 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.[28]

An impalastotting

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 therut,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 theSerengeti National Parkshowed that in 94% of the males, territoriality was observed for less than four months.[17]

The impala is an important prey species for Africa's largecarnivores,such ascheetahs,leopards,wild dogs,lions,hyenas,crocodilesandPython s.The antelope displays two characteristic leaps – it can jump up to 3 m (9.8 ft), over vegetation and even other impala, covering distances of up to 10 m (33 ft); 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 (stotting) and then rebounds. It leaps in either manner in different directions, probably to confusepredators.[13][29]At times, the impala may also conceal itself in vegetation to escape the eye of the predator.[30]The most prominent vocalisation is the loudroar,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 2 km (1.2 mi) away.[17]Scent gland secretions identify a territorial male.[31]Impalas are sedentary; adult and middle-aged males, in particular, can hold their territories for years.[17]

Parasites[edit]

Impala have a symbiotic relationship withoxpeckers.

Commonixodidticks collected from impala includeAmblyomma hebraeum,Boophilus decoloratus,Hyalomma marginatum,Ixodes cavipalpus,Rhipicephalus appendiculatusandR. evertsi.[32][33][34]InZimbabwe,heavy infestation by ticks such asR. appendiculatushas proved to be a major cause behind the high mortality of ungulates, as they can lead totick paralysis.Impala have special adaptations for grooming, such as their characteristic dental arrangement, to manage ticks before they engorge; however, the extensive grooming needed to keep the tick load under control involves the risk of dehydration during summer, lower vigilance against predators and gradual wearing out of the teeth. A study showed that impala adjust the time devoted to grooming and the number of grooming bouts according to the seasonal prevalence of ticks.[32]

Impala are symbiotically related tooxpeckers,[35]which feed on ticks from those parts of the antelope's body which the animal cannot access by itself (such as the ears, neck, eyelids, forehead and underbelly). The impala is the smallest ungulate with which oxpeckers are associated. In a study it was observed that oxpeckers selectively attended to impala despite the presence of other animals such asCoke's hartebeest,Grant's gazelle,Thomson's gazelleandtopi.A possible explanation for this could be that because the impala inhabits woodlands (which can have a high density of ticks), the impala could have greater mass of ticks per unit area of the body surface.[36]Another study showed that the oxpeckers prefer the ears over other parts of the body, probably because these parts show maximum tick infestation.[37]The bird has also been observed to perch on theuddersof a female and pilfer itsmilk.[38]

Licerecorded from impala includeDamalinia aepycerus,D. elongata,Linognathus aepycerusandL. nevilli;in a study,ivermectin(a medication against parasites) was found to have an effect onBoophilus decoloratusandLinognathusspecies, though not onDamaliniaspecies.[39]In a study of impala in South Africa, the number ofwormsin juveniles showed an increase with age, reaching a peak when impala turned a year old. This study recorded worms of genera such asCooperia,Cooperoides,Fasciola,Gongylonema.Haemonchus,Impalaia,LongistrongylusandTrichostrongylus;some of these showed seasonal variations in density.[40]

Impala show high frequency ofdefensive behaviourstowards flying insects.[41]This is probably the reason for Vale 1977 and Clausen et al 1998 only findingtrace levelsof feeding byGlossina(tsetse fly) upon impala.[41]

Theileriaof impala inKenyaare notcross infectioustocattle:Grootenhuis et al 1975 were not able to induce cattle infection and Fawcett et al 1987 did not find it naturally occurring.[42]

Diet[edit]

A herd grazing inMaasai Mara

Impalabrowseas well as graze; either may predominate, depending upon the availability of resources.[43]The diet comprisesmonocots,dicots,forbs,fruits andacaciapods (whenever available). Impala prefer places close to water sources, and resort tosucculent vegetationif water is scarce.[17]An analysis showed that the diet of impala is composed of 45% monocots, 45% dicots and 10% fruits; the proportion of grasses in the diet increases significantly (to as high as 90%) after the first rains, but declines in thedry season.[44]Browsing predominates in the late wet and dry season, and diets are nutritionally poor in the mid-dry season, when impala feed mostly on woody dicots.[13][45]Another study showed that the dicot proportion in the diet is much higher in bachelors and females than in territorial males.[46]

Impala feed on soft and nutritious grasses such asDigitaria macroblephara;tough, tall grasses, such asHeteropogon contortusandThemeda triandra,are typically avoided.[47]Impala on the periphery of the herds are generally more vigilant against predators than those feeding in the centre; a foraging individual will try to defend the patch it is feeding on by lowering its head.[48]A study revealed that time spent in foraging reaches a maximum of 75.5% of the day in the late dry season, decreases through the rainy season, and is minimal in the early dry season (57.8%).[49]

Reproduction[edit]

Males lock horns in a mating fight
Two males fighting fordominance

Males aresexually matureby the time they are a year old, though successful mating generally occurs only after four years. Mature males start establishing territories and try to gain access to females. Females can conceive after they are a year and a half old;oestruslasts for 24 to 48 hours, and occurs every 12–29 days in non-pregnant females.[30]The annual three-week-long rut (breeding season) begins toward the end of thewet season,typically in May.Gonadalgrowth andhormoneproduction in males begin a few months before the breeding season, resulting in greater aggressiveness and territoriality.[17]Thebulbourethral glandsare heavier,testosteronelevels are nearly twice as high in territorial males as in bachelors,[50]and the neck of a territorial male tends to be thicker than that of a bachelor during the rut. Mating tends to take place between full moons.[17]

Sounds of rutting male

Ruttingmales fight over dominance, often giving out noisy roars and chasing one another; they walk stiffly anddisplaytheir neck and horns. Males desist from feeding and allogrooming during the rut, probably to devote more time to garnering females in oestrus;[51]the male checks the female's urine to ensure that she is in oestrus.[52][51]On coming across such a female, the excited male begins thecourtshipby pursuing her, keeping a distance of 3–5 metres (9.8–16.4 ft) from her. The male flicks his tongue and may nod vigorously; the female allows him to lick her vulva, and holds her tail to one side. The male tries mounting the female, holding his head high and clasping her sides with his forelegs. Mounting attempts may be repeated every few seconds to every minute or two. The male loses interest in the female after the first copulation, though she is still active and can mate with other males.[17][26]

Gestation lasts six to seven months. Births generally occur in the midday; the female will isolate herself from the herd when labour pain begins.[53]The perception that females can delay giving birth for an additional month if conditions are harsh may however not be realistic.[54]A single calf is born, and is immediately concealed in cover for the first few weeks of its birth. The fawn then joins a nursery group within its mother's herd. Calves are suckled for four to six months; young males, forced out of the group, join bachelor herds, while females may stay back.[17]

Distribution and habitat[edit]

A herd in Tanzania
Impala inhabit woodlands.

The impala inhabits woodlands due to its preference for shade; it can also be found on the interface (ecotone) between woodlands and savannahs. Places near water sources are preferred. In southern Africa, populations tend to be associated withColophospermum mopaneandAcaciawoodlands.[17][43]Habitat choices differ seasonally –Acacia senegalwoodlands are preferred in the wet season, andA. drepanolobiumsavannahs in the dry season. Another factor that could influence habitat choice is vulnerability to predators; impala tend to keep away from areas with tall grasses as predators could be concealed there.[47]A study found that the reduction of woodland cover and creation of shrublands by theAfrican bush elephantshas favoured impala population by increasing the availability of more dry season browse. Earlier, theBaikiaeawoodland, which has now declined due to elephants, provided minimum browsing for impala. The newly formedCapparisshrubland, on the other hand, could be a key browsing habitat.[55]Impala are generally not associated withmontanehabitats;[13]however, inKwaZulu-Natal,impala have been recorded at altitudes of up to 1,400 metres (4,600 ft)above sea level.[43]

The historical range of the impala – spanning across southern and eastern Africa – has remained intact to a great extent, although it has disappeared from a few places, such asBurundi.The range extends from central and southern Kenya and northeasternUgandain the east to northern KwaZulu-Natal in the south, and westward up to Namibia and southern Angola. The black-faced impala is confined to southwestern Angola andKaokolandin northwestern Namibia; the status of this subspecies has not been monitored since the 2000s. The common impala has a wider distribution, and has been introduced in protected areas inGabonand across southern Africa.[1]

Threats and conservation[edit]

Impalas ofKruger National Park,RSA
Impala tracks

TheInternational Union for Conservation of Nature and Natural Resources(IUCN) classifies the impala as aspecies of least concernoverall.[1]The black-faced impala, however, is classified as avulnerable species;as of 2008, fewer than 1,000 were estimated in the wild.[56]Though there are no major threats to the survival of the common impala, poaching and natural calamities have significantly contributed to the decline of the black-faced impala. As of 2008, the population of the common impala has been estimated at around two million.[1]According to some studies,translocationof the black-faced impala can be highly beneficial in its conservation.[57][58]

Around a quarter of the common impala populations occur in protected areas, such as theOkavango Delta(Botswana);Masai MaraandKajiado(Kenya);Kruger National Park(South Africa); theRuahaandSerengeti National ParksandSelous Game Reserve(Tanzania);Luangwa Valley(Zambia);Hwange,SebungweandZambezi Valley(Zimbabwe). The rare black-faced impala has been introduced into private farms in Namibia and theEtosha National Park.Population densities vary largely from place to place; from less than one impala per square kilometre inMkomazi National Park(Tanzania) to as high as 135 per square kilometre nearLake Kariba(Zimbabwe).[1][59]

References[edit]

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External links[edit]

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