Impala, Aepyceros melampus
Images of Impala
WHAT IT IS
A one-of a-kind antelope. No close relatives. Graceful build, long neck, limbs evenly developed and slender. Male wt 117-167 lb (53-76 kg), ht 30-36 in (75-92 cm); Female wt 88-117 lb (40-53 kg), ht 28-34 in (70-85 cm). Horns: male only; S-shaped and wide-set, 18 to 37 in (45-91.7 cm), strongly ridged but comparatively thin; far larger in East African than in southern African populations. Tail: hock-length, bushy. Coat: smooth and shiny. Color: two-toned: tan torso and limbs with a reddish brown saddle; vertical black stripes down tail and thighs, hoof joints and ear tips black; white belly, throat, lips, line over eye, inside ears, and tail underside; sexes and young colored alike. Scent glands: on rear feet above hooves, marked by black tuft, and on forehead skin of adult males. Teats: 4.
WHERE IT LIVES
Southern Savanna, from central Kenya and Rwanda to northern Natal, west to Namibia and southern Angola. Highly successful antelope, dominant in its chosen habitat.
ECOLOGY
An edge species that prefers open woodland bordering short to medium grassland, well-drained soil with firm footing and no more than moderate slope. Usually lives near water but can go without drinking. These requirements cause impalas to have an irregular and clumped distribution.
A grazer/browser: usually grazes while grasses are growing, browses on foliage, herbs, shoots, and seedpods when grasses are dry. Unusually adaptable, impalas can be primarily a browser in one area and a grazer in another, enabling it to thrive in places where overstocking and burning have caused perennial grasses to be replaced by bushes. In optimum habitat, reaches densities of 554/miles square (214/km square).
GOOD PLACES TO SEE IT
Most national parks and reserves within its range, notably Samburu GR, Nairobi Park, Masai Mara NR, Kenya; Serengeti, Tarangire, and Manyara NP, Tanzania; Hwange NP, Zimbabwe; Chobe NP, Moremi GR, Botswana; Kruger NP, Umfolozi and Mkuzi GR, South Africa.
ACTIVITY
Mainly daytime. Spends night resting in the most open available terrain, except one feeding bout starting before midnight and lasting until 3 or 4 AM. But highly active on moonlight nights during rut. Usual peaks of social activity and herd movements early and late in day.
SOCIAL/MATING SYSTEM
A strictly territorial animal when it counts.- only landlords get to reproduce. Yet the very existence of territoriality in this species was long doubted by some researchers, mainly because of the dry-season attenuation or suspension of territorial behavior, when impalas are often found in mixed herds, and a rapid turnover of territorial males during the breeding season. The root cause of the confusion is the impala's naturally clumped distribution, with bachelor males in proximity to female herds at all seasons. In fact, male sexual competition is unusually intense in the impala because female impala herds tend to be large, giving owners of good territories many reproductive opportunities. From 6 to 20 females and young is a minimum average-herds of 50 to I 00 are common.
Marking of 443 impalas in Zimbabwe's Sengwa Research Area led to the discovery that females there live in separate, stable clans of 30 to 120 individuals which occupy traditional home ranges of 198 to 445 acres (80-180 hectares), Although clan ranges overlap as much as 31% late in the dry season and mixing sometimes occurs, very few females join a different clan-whereas virtually all males do, thereby avoiding inbreeding.
Female herds are notable for close packing, uniformity, synchronized activities, and lack of a regular rank order or leadership. There is little aggression and great variation in herd composition from day to day as clan members come and go.
Territory size varies with population density, season, habitat quality, location, and individual prowess. Holdings are smallest at high density in good habitat during the rainy/breeding season. They averaged 27 acres (10.8 hectares) during the rutting peak in Sengwa, at a density of 129 to 176 impalas/miles square (50-68/km square)-tiny compared to the average 143-acre (58 hectares) properties Serengeti impalas defend in the dry season at a density of 83 impalas/miles square (32/km square).
Actively territorial males spend up to V4 of their time shepherding females, time that would otherwise be spent feeding and digesting. Keeping bachelor males away and cutting out juveniles whose horns betray their sex add to the energy they expend. In the East African populations, where breeding continues most of the year, few males last even three months before losing condition and being replaced. They join bachelor herds to recuperate and try again-but are only ready after rising to the top of the bachelor hierarchy. Impalas become attached to the place they first win a territory and when staging a comeback try to regain their former property, so more often than not, the male who replaces the current occupant is a former owner.
HOW IT MOVES
Famous jumpers, alarmed impalas high-jump 10 ft (3 m) and broad-jump 36 ft (11 m). To escape predators that stalk within pouncing range, a whole herd explodes in all directions. More rarely, impalas perform a unique and equally spectacular high jump. As a runner, the impala is neither very fleet nor enduring; indeed, dependence on cover to escape spotted hyenas, wild dogs, and cheetahs may be important in its habitat preferences.
REPRODUCTION
Southern impala: 3-week rut end of the rainy season, apparently triggered by the full moon; beginning date varies by up to 20 days from year to year; vigorous territorial behavior limited to the few months preceding and following the mating peak. East Africa: breeding season more extended, although most females conceive late in the rainy season. More sustained sexual competition may explain the bigger horns of East African impalas.
Females conceive at about, 1.5 years; males, though adolescent as yearlings, only begin breeding after acquiring territories in their fourth year. Gestation 194 to 200 days.
OFFSPRING AND MATERNAL CARE
Late dry-season birth peak (Sept. or Oct). Some mothers bring fawns only 2 to 3 days old into the herd, where they associate with other newborns in cr@ches. Juveniles rest, move, play, and groom with one another, only seeking mothers to nurse or for protection. Weaning complete as early as 4 to 5 months; by then males' horns have emerged, exposing them to increasing aggression by breeding males. Males in East African populations all end up in bachelor herds by 8 months.
PREDATORS
Wherever abundant, impalas are a mainstay of all the large predators; fawns are small enough to be carried off by martial eagles.
IMPALA BEHAVIOR GUIDE
Expect to see and hear
Usual context and meaning
Territorial Advertising
Adult male standing or lying, alone or apart from herd. Advertises presence of a territorial male.
Proud posture. Impala version of the erect posture (particularly statuesque).
Urination and defecation in sequence on dung midden. Visual display and scent-marking. Middens located on paths, roadways, other bare ground, and in the 15-30 yd neutral zone between adjoining territories.
Rubbing forehead on tree stem; often followed by homing. Visual display and scent-marking performed by territorial males and top-ranking bachelors.
Vegetation-homing. Advertises aggressive mood and high status. Often performed by territorial males, especially during interactions with potential challengers.
Roaring display: tail raised exposing white underside, while giving 1-3 explosive snorts, followed by 2-10 deep, guttural grunts, audible up to a mile. Also produced while in motion, as when chasing intruding males and driving females. Performance peaks during rut, by bachelor as well as territorial males.
Aggression
Standing or walking stiffly in proud posture, usually facing receiver head turned away. Display of dominance to rival males or to females trying to exit property.
Medial-hom threat.
High-hom threat. Presents forehead skin for inspection by inferiors; equals respond in kind.
Low-horn threat.
OTHER ACTIONS ASSOCIATED WITH DOMINANCE/THREAT DISPLAYS
Head-tossing, vegetation-homing, tail-raising/-spreading, displacement activities.
Head-dipping. Exaggerated nodding.
Jumping toward opponent. Feinted attack.
Air-cushion fights. Going through the motions of fighting.
Yawning and moving jaw side-to-side. Seems to indicate tension, but significance unknown.
Tongue-flicking. Also seen in courtship.
Head-low posture. Defensive threat, response of inferior to superior's threat.
FEMALE AGGRESSION
Head-dipping, butting.
Submission
Moving away in head-low posture. Avoidance of superior, when threatened or supplanted.
Approaching and sniffing adult male's forehead. Behavior of subordinate (checking skin-gland secretion)
Flight. Response of inferior or defeated rival to pursuit.
Displacement Activities
Grazing, scratching with hind feet, scratching with horn tips, scraping with incisors.
Sociable Behavior
Social grooming: tit-for-tat incisor grooming of the head and neck, between all classes, including adult males. After initial approach and nose-to-nose contact, a pair stands facing with heads turned 45 degrees. One scrapes the other 4-8 times, then stops and waits for response in kind. Bouts typically include 6-12 exchanges before one or both move away.
Courtship
Lowstretch ± tongue-flicking. Posture of territorial male checking out females, often prompted by female urination posture.
Female urination posture, with tail spread. Femalesurinate when they feel like it, not in response to male approach or display.
Urine-testing. Checking female reproductive status; mouth open but no pronounced grimace.
COURTSHIP STAGES
Pursuit in lowstretch ± roaring, snorting, and wheezing. Male exerts himself to separate female from herd.
Female tries to hide in herd, circles back each time male drives her out.
Close following and tongue-flicking ± head-nodding. Mating march. Female ready to mate permits male to lick her rear.
POSTMATING BEHAVIOR
Male often chases males, herds females and performs roaring display.
Mother and Offspring
Described in Mother and Offsrpring.
Play
High-jumping. Series of soaring bounds, like exaggerated stotting, descending vertically and throwing hind legs high in air.
Chasing, cavorting, sparring.
Response to Predators
Alert posture, stamping, alarm-snorting, other nervous behavior.
Impalas spend much time in bushy habitat, are unusually alert to possible danger.
Flight-intention movement. sudden upward head movement with neck stretched forward. Other impalas often react by taking flight.
Leaping and scattering. Startled herd members explode in all directions.
Reprinted from "The Safari Companion" by Richard Estes
nature@nature-wildlife.com