Kenya's Tana River divides the range of East Africa's two
types of oryx the beisa oryx (Oryx g. beisa) and the
fringe-eared oryx (Oryx g. callotis). The fringe-eared oryx
ranges from Kenya to central Tanzania. The beisa oryx ranges
from Ethiopia through Somalia into northeastern Uganda and
The oryx is a large antelope of striking appearance
with long, spearlike horns. It has a thick, horselike neck with
a short mane and a compact, muscular body. A defined pattern of
black markings that contrast with the white face and
fawn-colored body are prominently displayed in dominance rituals
to emphasize the length of horns and strength of the shoulder.
The head is marked with black triangular patches and broad
black stripes that extend from the base of the horns over the
eyes to the cheeks. A ring of black encircles the throat and
runs down the neck to the chest. The ears end in a black tip (a
black tassel hangs from the ear tip of the fringe-eared oryx). A
narrow black stripe runs along the spine, and another one
separates the lower flank from the white underparts of the body.
The white forelegs have a black ring above the knee and a black
patch below. The black tail tassel reaches to the hocks.
The oryx's ringed horns are up to 30 inches long, making them
formidable weapons. The female's horns are often longer and
thinner than the male's.
Originally, various oryx species were found in all of Africa's
arid regions. One species that occurred on the Arabian Peninsula
was exterminated recently but has now been reintroduced into the
wild from captive stock. Well adapted to the conditions of their
hot, arid habitats, oryx can live as long as 20 years.
The social system of the oryx is unusual in that
nonterritorial males live in mixed groups with females, or with
females and their young. Males that dominate are territorial to
a degree, marking their areas with dung deposits. Groups are
composed of 10 to 40 males and females of all ages and both
sexes; herds of up to 200 are common in some East African
The dominance hierarchy among oryx is based on age and size.
As they grow, calves test one another in what look like games,
though in reality are tests of strength. As the hierarchy
becomes established, the need to fight is reduced. Ritual
displays replace actual contact, except when evenly matched
individuals may have to fight to establish their rank. Along
with lateral displays, oryx perform a slow, prancing walk and
sometimes break into a gallop. When several males are making
these displays, they may clash horns.
Herd composition in the wild constantly changes according to
need. Oryx wanting to drink, for example, form a group to go to
water, or females with young form a group that moves more
slowly. The result is a social system that allows for individual
needs but retains the advantage of group living. Oryx range
widely over a large area, but their keen sense of smell alerts
them to rain in the area, so that groups quickly assemble, often
in herds of 200 or more, to feed on new growth.
Oryx typically feed in early morning and late afternoon and
sometimes on moonlit nights. Their diets consists mainly of
coarse grasses and browse from thorny shrubs. In desert areas
they consume thick leaved plants, wild melons, as well as roots
and tubers they dig out of the ground. They may drink if water
is available but can survive days or even weeks without it.
Plants growing in arid areas inhabited by oryx have also
adapted to the hot, dry conditions and either store water or
have mechanisms to prevent excess loss. Plants collect dew,
gradually releasing it during the hotter parts of the day. Some
plants increase their water content by 25 to 40 percent, so when
oryx feed late at night or early in the morning, it provides
them with both food and water.
A female leaves the herd to give birth and hides the calf for 2
or 3 weeks, visiting a few times a day to nurse it. The newborn
is an inconspicuous brown color. The black markings begin to
appear when the calf is ready to return to herd with its mother.
Calves are suckled for 6 to 9 months and reach maturity at 18 to
24 months. Most young males migrate out of their natal group to
join other groups.