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Oryx belong to the Hippotragini, the
family of horse-like antelopes. While there are only three
species of oryx there are five distinct forms. The southern
and east African species of oryx occurs in three forms or
sub-species; the gemsbok (Oryx gazella gazella), inhabits
the Kalahari system of southern Africa; the beisa oryx (O.
g. beisa) is found in the large arid area of Somalia and
eastern Africa with the closely related fringe-eared oryx
(O. g. callotis) in an adjacent range divided by the Tana
river in Kenya. The remaining two forms are distinct
species; the scimitar-horned oryx, (O. dammah), once roamed
across the Sahara desert but is today thought to be extinct
in the wild, while the Arabian peninsula is the home of the
Arabian or white oryx (O. leucoryx) reintroduced first to
Oman in 1982 and then Saudi Arabia in 1995.
All forms of oryx occupy either
semi-arid or arid areas. The gemsbok's range may have an
annual rainfall of between 50 mm to 250 mm while in East
Africa the fringe-eared and beisa oryxes live in bush land
savannahs that have up to 300 mm rain a year. However, the
driest ranges are occupied by the two northern species. In
former times the scimitar-horned ranged through the Sahara
desert's central hyper-arid zone where it migrated
seasonally into the true desert and the southerly wooded
steppes. The habitat of the Arabian oryx encompasses various
desert types such as sand dunes, stony plains and dry
drainage courses known as wadis. The habitat of this species
is consistently hotter and drier than that of any other oryx.
Mean annual total rainfall is less than 50 mm for much of
the interior of Arabia and many consecutive years may be
rainless.
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The size and appearance of the different
forms of oryx is related to the aridity of their ranges. The
gemsbok is the largest form and may weigh over 200 kg while
a large male Arabian oryx might weigh just 100 kg. The
gemsbok is a relatively dark form while the Arabian oryx is
a uniform white, while the flank stripe is absent or only an
indistinct smudge. The lower limbs are a chocolate brown to
black with the exception of pure white patterns. Males and
females present almost identical silhouettes, but adult
males weigh at least 10% more than females.
Herds in African species of oryx
normally contain approximately equal numbers of adult males
and females while Arabian oryx herds may contain several
females but rarely more than one adult male. Groups will
also contain following calves and immatures. Bachelor herds,
as in many antelopes, are absent or have been seen rarely.
Single territorial males are seen in gemsbok, fringe-eared
oryx and Arabian oryx. A dominance hierarchy involving both
sexes is found in herds of each species.
The oryx is renowned for its ability to
survive in hot, dry areas without drinking water for months,
if not years and the recorded patterns of distribution in
the Sahara, the Kalahari desert, East Africa and in Arabia
all confirm that drinking must be rare. However, most
species are likely to drink when offered water. For example
in Oman, wild-born Arabian oryx will drink water after
rainfall. Research suggests that the oryx may have a lower
water requirement than even the camel.
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