Impala
The graceful impala is a slender, medium-sized antelope
so adaptable that it is found from southern Africa to the northern
limits of East Africa.
Physical Characteristic
The body is reddish-brown with white hair inside
the ears, over each eye and on the chin, upper throat, underparts
and buttocks. A narrow black line runs along the middle of the lower
back to the long tail, and a vertical black stripe appears on the
back of each thigh. Unlike other antelopes, impalas have large, brushlike
tufts of long, coarse black hair that cover a scent gland located
just above the heel on each hind leg.
Habitat
Impalas are found at grassland and woodland edges,
usually very close by water.
Behavior
Their social organization allows impalas to adapt
to prevailing environmental conditions. When food is plentiful, the
males become territorial. In home ranges averaging 3 square miles,
six to eight dominant males set up territories. They stand with erect
posture, rub scent from face glands and make dung heaps to mark their
territory.
The females form herds of 10 to 50 or more and wander in and out
of male territories. If they start to leave the territory, the male
tries to herd them back to the center, or he feigns danger just
beyond his boundary by taking a stance normally used as a warning
sign. He tries to mate with females in estrus and defends his territory
from challenging males. Bachelor males are allowed to remain in
male territories if they ignore the females.
The territorial male's challenger will have worked his way up through
the hierarchy of the bachelor group until he becomes the dominant
male. He then leaves the group and challenges a territorial male
through horn duels, in which the males approach one another with
slow, deliberate steps. At a signal, such as swiveling the eyeballs
to show the whites or slightly nodding the head, they rush forward
and clash horns, attempting to throw one another off balance. Although
fighting can be fatal, males are protected by exceptionally thick
skin over vulnerable areas. It is not the length of horn that gives
a male the advantage but his condition and weight. When a territorial
male begins to lose weight from his frantic activity, he is defeated
and must return to the bachelor group to recuperate. There are times,
however, when this territorial system is not maintained. In drier
years the animals have to travel further to obtain food, and many
smaller herds of females form. They move in and out of the territories
so often that the males are very quickly exhausted. When this happens,
territories are abandoned, and large, mixed tranquil herds of females
and males form. When feed conditions improve, impalas revert to
the territorial system.
Diet
Impalas eat tender young grass shoots in the wet season
and herbs and shrubs at other times. During the dry season they must
drink daily.
Caring for the Young
In East Africa young are born year round, but birth
peaks usually coincide with the rains. The female leaves the herd
and seeks a secluded spot to bear her fawn. After giving birth she
cleans the fawn and eats the afterbirth. If the fawn is born at a
time when there are few other young around, the mother will stay with
it in seclusion spot for a few days or even leave it lying out for
a week or more before returning to the herd. If there are many other
fawns, she may take hers back to the herd in a day or two, where a
nursery group may form. Because predators have more difficulty selecting
an individual from a nursery group, the fawns are safer there.
The young are suckled for 4 to 6 months and grow rapidly, reaching
maturity at a little over a year. The young males, however, are
evicted from their mothers' groups when they are 6 months old, staying
around the edges of the herd until they join a bachelor group. During
this transition period they are most vulnerable to predators. Males
will not be mature enough to hold a territory until they are 5 or
6 years old.
Predators
The young are killed by jackals and the smaller
cats, baboons, eagles and pythons. When in danger, impalas will "explode"
in a magnificent spectacle of leaping. In their zig-zag leaps, they
often jump over and across their companions, probably to confuse predators.
They perform a high kick of the hind legs, a movement thought to release
scent from the glands on the heels, making it easier for them to stay
together.
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