The Biology, Husbandry and Conservation Scimitar-horned Oryx ...

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Part 2: Husbandry Guidelines
more peaceful bachelor group. However, this is not an appropriate method because it is not
possible for the animals to contribute to the captive breeding programme after the operation.
The key factors dictating levels of aggression in bachelor groups appear to be available space,
group size, and age of individuals:
Problems tend to occur when space is limited and the group size is small. If the enclosure is
large, the animals are able to avoid one another. If there are many animals in the group, the
attention of the dominant male is directed towards many opponents, and so attacks are not
concentrated on any particular individual (Krebs and Davies, 1993). This is analogous to several
bachelors entering the territory of a conspecific dominant male and creating a situation in which
the energy expenditure needed to repel those incursions is too great (Geist, 1968; Gosling,
1986).
In addition, problems will tend to occur when all males are greater than 22.5 months in age
and are sexually mature. Conversely, an obvious stratification of ages should produce a
mostly peaceful group. If one animal is about two years older than its group members, it is
able to hold the alpha position unchallenged. Moreover, this animal will act as peacemaker
and prevent aggression amongst other members of the group (Mungall & Sheffield, 1994;
Engel, 1997a).
In bachelor groups, there is no behavioural difference between individuals that have already
produced offspring and those that have not been used for breeding. Neither the presence of
females of other bovid species, nor a lack of linearity in the rank order affects the bachelor
group negatively (Engel, 1997a).
Assuming the above points are taken into consideration, the formation of bachelor groups is
highly recommended, particularly as all-male group may play an important role in the
socialisation of young males. In mixed herds, the lower ranking male adopts the female role in
mating behaviour between two males. In bachelor groups there is no such correlation between
rank and role. This supports the hypothesis that young male scimitar-horned oryx in a bachelor
herd perfect their sexual behaviour through practical training. Young subdominant males in
mixed groups do not have this opportunity. Furthermore, it is evident that learning is more
important in all-male groups than the demonstration of dominance (Engel, 1997a).
A final observation is that the level of aggression reported in all-male groups of scimitarhorned
oryx may be a particular phenomenon of artificially well-fed zoo populations. In the
wild, scimitar-horned oryx live in semi-arid and desert habitats where they spend most of
their time searching for food, and by the end of the hot season they are usually in very poor
condition (Gillet, 1966a; Newby, 1974). Bachelor groups in particular are forced to live in the
least favourable habitats (Bigalke, 1974; Gosling, 1974; Montfort-Braham, 1975; Attwell,
1982). Although the mechanisms by which diet modulates gonadotrophin secretion are
unclear, there is substantial evidence for a positive correlation between nutrition and
testosterone levels (Setchell et al., 1965; Millar & Fairall, 1976; Gauthier & Couland, 1986).
Furthermore, there is a positive correlation between testosterone and social aggressive
behaviour (Illius et al., 1976, 1983; Sapolsky, 1982, 1993; Bouissou, 1983; Sachser & Pröve,
1986). It may be possible to reduce aggression in zoo-based bachelor groups by modifying the
diet. This would be in perfect accordance with what is known about the ultimate and
proximate factors of all-male groups (Engel, 1997a).