C. R. Biologies 326 (2003) S158–S165
Reintroducing antelopes into arid areas: lessons learnt
from the oryx in Saudi Arabia
Pascal Mésochina ∗
, Eric Bedin, Stéphane Ostrowski
N.W.R.C/N.C.W.C.D, P.O. Box 1086, Taif, Saudi Arabia
Abstract
We focus on constraints faced by antelopes reintroductions in arid environments, and propose keys to enhance their success,
using the oryx project in Saudi Arabia as example:
(1) Monitoring and management of reintroduced populations appear more important than the number of released animals;
(2) Because of the low accuracy of population size estimators, we recommend to implement a continuous monitoring and to
use several estimators to assess the reintroduced population size;
(3) Reintroduction schedule should take into account the unpredictability of food resources in arid environments;
(4) The re-establishment of desert antelopes depends as a priority on the enforcement of regulations to avoid poaching.
To cite this article: P. Mésochina et al., C. R. Biologies 326 (2003).
 2003 Académie des sciences. Published by Éditions scientifiques et médicales Elsevier SAS. All rights reserved.
Résumé
Réintroduire les antilopes en milieu aride : enseignements de l’oryx en Arabie Saoudite. Nous présentons les difficultés
inhérentes aux réintroductions d’antilopes en milieu aride, et proposons quelques clés pour améliorer leur succès, en s’appuyant
sur la réintroduction de l’oryx (Oryx leucoryx) en Arabie Saoudite :
(1) Le suivi et la gestion des populations réintroduites apparaissent plus importants que le nombre d’individus relâchés ;
(2) La difficulté d’évaluer la taille des populations réintroduites peut être compensée par un suivi continu et l’exploitation de
plusieurs estimateurs ;
(3) La flexibilité du calendrier des réintroductions est rendue primordiale par l’imprévisibilité des ressources alimentaires en
milieu désertique ;
(4) Le rétablissement de populations d’antilopes désertiques dépend prioritairement de l’application de mesures anti-
braconnage.
Pour citer cet article : P. Mésochina et al., C. R. Biologies 326 (2003).
 2003 Académie des sciences. Published by Éditions scientifiques et médicales Elsevier SAS. All rights reserved.
Keywords: Arabian oryx; antelopes; desert; Oryx leucoryx; reintroduction success
Mots-clés : antilopes ; désert ; oryx d’Arabie ; Oryx leucoryx ; succès de réintroduction
* Corresponding author.
E-mail address: Mesochina@nwrc-sa.org (P. Mésochina).
1631-0691/$ – see front matter  2003 Académie des sciences. Published by Éditions scientifiques et médicales Elsevier SAS. All rights
reserved.
doi:10.1016/S1631-0691(03)00053-2
P. Mésochina et al. / C. R. Biologies 326 (2003) S158–S165 S159
1. Introduction
Nearly half of the antelope species (46%) are included
by the International Union for the Conservation
of Nature (IUCN) in the Red List of threatened
species [1]. Among the species that occur in arid environments,
this ratio increases to around 65%, and
reaches 92% among the 13 species surviving in the
harsh conditions of Sahara and Arabian deserts (Table
1).
Among the numerous tools used in conservation to
re-establish endangered species (creation of protected
areas, captive-breeding,...), reintroduction is a commonly
used, popular and suitable conservation procedure
for vertebrates [2] which becomes a necessity
once the species has been extirpated from the wild [3].
Many studies have emphasized the importance of
maintaining genetic diversity in the reintroduced populations
(e.g. [4–6]). After presenting some conservation
genetic aspects of the Arabian oryx reintroduction,
we focus on three factors recognized as determinant
to increase the probability of success of vertebrate
reintroductions [2,4,7,8], and evaluate how they apply
to the case of the Arabian oryx reintroduction in Saudi
Arabia:
(1) The number of reintroduced animals;
(2) The post-release monitoring of reintroduced pop-
ulations;
(3) The quality of recipient areas in term of coverage
of vital requirements of the species.
2. The case of the Arabian oryx (Oryx leucoryx)
The Arabian oryx which formerly occurred throughout
Arabian peninsula deserts was extirpated from the
wild by hunting in the early 1970s [9]. The species
was first reintroduced in Oman in 1982 [10]. In Saudi
Arabia, the Arabian oryx was first released in 1990
into Mahazat as-Sayd [11], a fenced steppe desert protected
area in west-central Saudi Arabia (2244 km2).
Since 1995, Arabian oryx have also been reintroduced
into ‘Uruq Bani Ma’arid, a sand dune protected area
(12 500 km2) which lies in the western Rub-al Khali,
one of the driest regions in the world [12].
The Arabian oryx is a social, large, white and
desert antelope (80–100 kg), which survives indefinitely
without access to drinking water in arid habitats
[13,14]. Classified as a mixed-feeder but predominantly
grazer [15,16], it can survive on poor
quality forage [17], and decides of its range use according
to the biomass and quality of forage available
[16], and its seasonal food requirements [13]. Presumably
because of the low food resources available in
deserts, the Arabian oryx lives at low densities (around
0.016 oryx/km2 in Oman in 1996 [10] and in ‘Uruq
Bani Ma’arid in 2001 [18]).
The climate of Saudi Arabia is characterized by
hot summers and mild winters. Air temperatures
in summer often exceed 45 ◦C [18,19]. The main
characteristic of climate is that rainfall is unpredictable
both spatially and temporally (i.e. precipitation at Mahazat
as-Sayd ranges from 38 mm in 1999 to 253 mm
in 1995).
3. Lessons from the reintroduction of Arabian
oryx
Reintroduction is defined as an attempt to establish
a species in an area which was once part of its
historical range, but from which it has been extirpated
or became extinct [3]. Three main factors increase
the probability of success of vertebrate reintroductions
[2,4,7,8], namely:
– The number of reintroduced animals;
– The post-release monitoring of reintroduced pop-
ulation;
– The quality of recipient areas in term of coverage
of vital requirements of the species.
Although not included in the analysis of Fischer and
Lindenmayer [2], Griffith et al. [4], and Wolf et al. [7,
8], based on mailing results or published papers surveys,
genetic diversity of the reintroduced population
may influence its re-establishment success (e.g. [4–
6]). For this reason, we present the genetic status of the
captive breeding herd hosted at the National Wildlife
Research Center (NWRC) before developing the three
salient key tenets of successful reintroduction.
3.1. Genetic management of Arabian oryx herd at the
NWRC
The goal of our management has been to maintain
the initial genetic diversity through careful breeding
S160 P. Mésochina et al. / C. R. Biologies 326 (2003) S158–S165
Table 1
IUCN conservation status of wild antelope species that occur in the Sahara and Arabian deserts [1,43]. nt = near threatened; cd = conservation
dependent
Species IUCN Status 1996 IUCN Status 2000
Gazella dama, dama gazelle Endangered Endangered
Gazella leptoceros, slender-horned gazelle Endangered Endangered
Gazella cuvieri, Cuvier’s gazelle Endangered Endangered
Gazella dorcas, dorcas gazelle Lower Risk – nt Vulnerable
Gazella subgutturosa marica, Arabian goitered gazelle Lower Risk – nt Vulnerable
Gazella gazella cora, Arabian mountain gazelle Lower Risk – cd Lower Risk – cd
Gazella rufifrons, red-fronted gazelle Vulnerable Vulnerable
Oryx leucoryx, Arabian oryx Endangered Endangered
Oryx dammah, scimitar-horned oryx Critically Endangered Extinct in the Wild
Addax nasomaculatus, addax Endangered Critically Endangered
Hemitragus jayakari, Arabian Tahr Endangered Endangered
Capra nubiana, Nubian Ibex Endangered Endangered
Ammotragus lervia, Barbary sheep Vulnerable Vulnerable
and to limit inbreeding level of animals to be reintro-
duced.
The degree of relatedness within the original oryx
herd of the NWRC is unknown, and the Arabian
oryx microsatellite loci discovered up to now are not
sufficiently polymorphic to carry out a large-scale
parentage inference analysis [20]. Consequently, we
considered original animals with unknown parents as
“founders” [21].
The policy implemented was to balance the 48
putative founder representations within each captive
generation (and reintroduced populations). Ultimately,
we built-up a captive oryx population recognized as
the most polymorphic of all captive herds (heterozygosity
varying between 0.425 and 0.785 [20]), with
the class of rare alleles (frequencies 0–0.1) being the
modal class (L-shaped allele frequency distribution),
suggesting that no recent management-related bottleneck
has occurred [20]. The NWRC herd is currently
composed of more than 240 individuals (Fig. 1).
However, recent genetic analysis have suggested
that perhaps as much as 50% of the neutral genetic
variation present in the pre-extinction population of
Arabian oryx is absent from contemporary populations
[20]. Yet, the high rate of intrinsic population
growth in reintroduced populations has suggested that
this “lack” of polymorphismdid not constraint population
establishment a least in the short term (e.g. mean
intrinsic growth rate of 40 and 43% before drought
period respectively in Mahazat as-Sayd and ‘Uruq
Bani Ma’arid; see also [22]). Indeed, a majority of
Fig. 1. Development of captive-bred Arabian oryx population at
the NWRC. Herd growth reduction is mainly due to reintroduction
effort increase since 1996.
the captive oryx populations in the Arabian peninsula
are essentially confronted with housing saturation difficulties
(Ostrowski, pers. com.) and infectious diseases
[23–25], often transmitted by neighbouring live-
stock.
3.2. Number of reintroduced animals
According to Fischer and Lindenmayer [2], Griffith
et al. [4], and Wolf et al. [7,8], vertebrate reintroductions
success is increased when more than 100 individuals
are released.
Between 1990 and 1993, we reintroduced 72 Arabian
oryx into the fenced Mahazat as-Sayd protected
area; animals derived from the captive breeding stock
held at the NWRC, and from foreign private or na-
P. Mésochina et al. / C. R. Biologies 326 (2003) S158–S165 S161
Fig. 2. Mahazat as-Sayd oryx population estimates between 1990 and 2001 using three different estimators. MPE: Minimum Population
Estimation (from field workers census); Transect: Transect count using Distance; MR: Mark-re-sighting index.
tional collections [11]. In 2001, we estimated the reestablished
population size at about 450 animals [26]
(Fig. 2).
Since 1995, 139 Arabian oryx issued from the
NWRC have been reintroduced into the ‘Uruq Bani
Ma’arid protected area [27]. By 2001, the population
had increased to 200–220 animals (Fig. 3). Further
releases are planned to avoid bottleneck phenomena in
case of prolonged demographic stagnation. It appears
at present premature to deem the success of this
reintroduction project.
In the case of a fenced, predator-free area like
Mahazat as-Sayd, or an unfenced protected area as
Yalooni in Oman (40 animals released [10]), the
number of animals released, lower than recommended
[2,4,7,8] did not seem to limit the oryx population re-
establishment.
3.3. Post-release monitoring of reintroduced
population
Monitoring of reintroduced populations is a key
factor to evaluate the success of reintroductions and
to implement management policies.
Because in arid environments, wild antelopes usually
survive at low densities, estimators of population
size have a low accuracy, owing to the small number
of individuals encountered during surveys. We observed
such inaccuracy even in the closed and highly
surveyed oryx population of Mahazat as-Sayd, where
coefficient of variation of transect estimators (Distance
software; [28]) often exceeded 50% [29] (Fig. 2).
We have tried two different strategies to offset this
weakness:
– We use three different methods of population size
estimation in Mahazat as-Sayd (Fig. 2): cumulated
births and deaths recorded by field workers, transect
counts and mark-re-sighting index [30]. This
monitoring effort allows us to cross-check convergent
indications, and to carry out surveys only
twice a year.
– In ‘Uruq Bani Ma’arid, we rely on an intensive
post-released population monitoring (e.g. 184
cumulative days spent in the protected area by
the field researcher in 2001). We also use aerial
surveys (18 aerial survey sessions were carried
out in 2001) to improve the monitoring efficacy
for these large desert antelopes. Transect
counts are not used because of the low number
of oryx encountered during surveys (density
of around 0.016 oryx/km2 in 2001 [18], against
0.20 oryx/km2 in Mahazat as-Sayd [26]), and hilly
ground. However, because during summer, oryx
aggregate (mean herd size is 4.3 during summer
and 2.5 during winter) in a small part of the re-
S162 P. Mésochina et al. / C. R. Biologies 326 (2003) S158–S165
Fig. 3. Estimated growth rates of the Arabian oryx population in ‘Uruq Bani Ma’arid protected area before and during drought period (r: mean
relative growth rate).
serve (around 1200 km2 [18]) where trees provide
them with shade, we use during this period total
count method coupled to a mark-re-sighting index
to estimate their number.
Monitoring also provides the basis to manage these
populations. Using data-driven assumptions for birth
rate, survival rate and carrying capacity, Treydte et
al. [31] developed a computer model to evaluate the
probability of extinction (frequency with which 100
initial populations fall to zero within 100 years) of the
predator-free Mahazat as-Sayd oryx population under
various management strategies. The probability of extinction
was high when no management was applied
to the population (probability of extinction varied between
0.3 and 0.92 according to combination of assumptions)
whereas removing all oryx above 70% of
carrying capacity provided the lowest probability of
extinction, and the lowest population size variation
whatever was the combination of assumptions. Management
appears therefore as an important aspect of
the long term persistence of this fenced reintroduced
population.
According to Fischer and Lindenmayer [2], the
probability of success of mammal reintroductions increases
if supportive measures are taken. However, the
supply of food and water during summer does not appear
as a viable option for the closed oryx population
of Mahazat as-Sayd protected area, as it would allow
the population to grow when density dependence
would normally be controlling numbers [31].
3.4. Quality of the reintroduction areas
It is recommended that reintroduction sites cover
the vital requirements of the reintroduced species and
that causes of its original decline are removed from
these sites [3].
3.4.1. Coverage of vital requirements
Arabian oryx require shade to survive during summer
and sufficient forage supply [32,33].
It is therefore important to select reintroduction
sites that can fulfill the summer shading requirements
of this species [32].
P. Mésochina et al. / C. R. Biologies 326 (2003) S158–S165 S163
Fig. 4. Illustration of the “feed-back” management process on Arabian oryx reintroduction according to biomass and quality of forage available.
Contrary to the preconceived idea that surface water
is a limiting factor of antelope populations dwelling
in deserts, it seems that these species are more dependent
on the preformed water in the forage than
on drinking water [13,14,33]. Indeed, Arabian oryx
may survive indefinitely without drinking water [13,
14]. Because biomass and quality of forage available
are strongly related to the occurrence of unpredictable
rainfall [34–37], the long term prediction of
forage availability and as a consequence of oryx release
schedule are difficult (Fig. 4).
The effect of rainfall on herbivore population dynamic
has been well documented (e.g. [31,34,37,38]).
Prolonged drought in arid habitat may lead to herbivore
population collapse (e.g. [39]). In ‘Uruq Bani
Ma’arid protected area, a severe drought period between
1997 and 2001 [18] has decreased the intrinsic
growth rate of the oryx population (Fig. 3).
3.4.2. Alleviation of causes of decline
3.4.2.1. Habitat degradation and interspecific competition.
Although habitat degradation and interspecific
competition did not appear to be responsible for
the oryx extirpation from the wild [40], they represent
a potential threat to the successful re-establishment of
wild populations.
Although lowly populated, it is likely that the
habitat used by the pre-extinction populations of
Arabian oryx has changed. In ‘Uruq Bani Ma’arid,
further habitat degradation has been minimized by
controlling the number of human settlements within
the reserve [11]. Tree cutting is a source of concern
because oryx need the shade provided by trees to
retreat from direct solar radiations in summer [32].
A ban on tree cutting inside the protected area must
be enforced, despite local bedus still use wood as
a source of energy. The recent development of ecotouristic
activities constitutes an additional concern
related to habitat degradation. The negative impact of
such activities on the protected area will have to be
evaluated and ultimately controlled.
Oryx compete on forage with camels. Levels of
tolerance still need to be addressed scientifically.
Although a certain level of competition is tolerable,
we suggest that it may become threatening under
the combined effect of drought conditions and oryx
population increase. Level of grazing control, by
limiting the number of domestic livestock permitted
inside the protected area, must rely on a quantitative
and scientifically-based approach.
3.4.2.2. The poaching threat. Over hunting is the
main cause of decline or extinction of desert an-
S164 P. Mésochina et al. / C. R. Biologies 326 (2003) S158–S165
telopes [40]. Although living at low densities in a vast
habitat, oryx are highly vulnerable to hunting. Their
destruction is eased by the fact that:
– They are conspicuous from a long distance (up to
3 km) because of their white and highly reflective
coat [33,41];
– They leave conspicuous tracks in the sandy areas
where they dwell;
– They display fairly little stamina when running
(presumably because of its high water and energy
cost);
– They can be easily chased by car when in open flat
areas;
– They have to shade under trees during summer
[32], and tree locations are known from local
inhabitants;
– They use to aggregate in areas where rainfall
occurred [36], also known from local inhabitants.
Until now, we have recorded seven poached oryx in the
‘Uruq Bani Ma’arid protected area. Althouth a marginal
cause of death (around 15% of all known mortalities),
we must remember that poaching foiled the
oryx re-establishment project in Oman. After reaching
a viable number of around 400 animals in 1996,
the reintroduced population collapsed to less than 100
animals by early 1999 [10]. Considering the different
causes of mortality in Oman, poaching has been the
main cause of death and the only reason for the Arabian
oryx population to collapse.
4. Perspectives
We may generalize the lessons learnt from the
Arabian oryx reintroduction in Saudi Arabia to desert
antelope reintroductions:
(1) Monitoring and management of desert antelope
reintroduced populations appear more important
than the number of released animals;
(2) Because of the low accuracy of desert antelope
population size estimators, we recommend to
implement an intensive monitoring and use a set
of estimators to assess the reintroduced population
size and growth rate;
(3) Timing of release must match the biomass and
quality of forage available. Because this parameter
is difficult to predict in an habitat where rainfall
is unpredictable, reintroduction plans must be
flexible;
(4) Long term reintroduction success of desert antelopes
is highly dependent on the enforcement
of regulations to avoid the hunting of these rare
species [40]. With the predicted climatic aridity
increase [42], this effort is of particular importance,
as animals will probably leave the relative
safety of their drying habitats and approach human
settlements.
Acknowledgements
We are very grateful to Dr. Joe Williams for useful
comments and criticisms on the manuscript.
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