The spatial distributions of 20 female and 15 male Arabian oryx Oryx leucoryx, reintroduced into the fenced Mahazat as-Sayd protected area (2,244 km2) in western Saudi Arabia between 1990 and 1994, were examined from their release until the end of 1999. Over this period we observed a westward shift in home range location of most male and female founder oryx to include the Rangers' Camp within core areas of activity, despite rain falling in patches throughout most of the reserve. Sporadic and unplanned availability of water had occurred at the Camp during several years. The pre-release enclosure was also located at the Camp, and high quality shading areas could be found underneath portacabins. Oryx that maintained independence of the Camp tended to be older individuals and those released in the first years (1990–1992). Concentration of oryx in the western part of the protected area and around the Camp could potentially reduce the effective carrying capacity of the reserve, change the social structure of the population, facilitate the transmission of disease, modify habitat in the form of a piosphere (a zone of attenuating animal impact away from a watering point) around the Camp, and reduce potential genetic flow within the reintroduced population. Whereas wild-born oryx were observed at the Camp, founders were disproportionately represented, suggesting that potential problems associated with dependence on the Camp may diminish as the total population increases and ages.

The distribution of the Arabian oryx Oryx leucoryx had declined markedly by the time European explorers documented distributions, and the species became extinct in the wild by the mid 1970s. Consequently, historical distribution records may be unreliable indicators of current habitat suitability for reintroductions. In this study diurnal behaviour of Arabian oryx was recorded within a central Saudi Arabian reintroduction site. Oryx were less active on warmer days due to an increase in shading (resting in shade) at the expense of feeding time; there was an inverse relationship between temperature and feeding. During hot conditions (maximum ambient temperature >40°C) some individuals spent <2 hours feeding during the day, compared with an average of 4.8 hours during cooler weather. This suggests the importance of shade trees to permit year-round occupancy in reintroduction sites. Selection of sites according to documented historical distribution may focus on tree-less areas, probably formerly part of the winter range. Absence of shade could result in migration out of the reserve, into areas where oryx risk being shot.

The crude protein content, water content and in vitro digestibility of grasses in the diet of the Arabian oryx Oryx leucoryx were investigated. In the main food species, Stipagrostis spp., levels of crude protein, water content and digestibility were generally highest in the flower component while in other species, leaf was the best quality food. Crude protein content, water content and digestibility were highly correlated and all declined exponentially following rainfall. Levels remained comparatively high, even during extended drought, largely because fog and dew-fall enabled some plants to continue to produce green leaf material. The crude protein content of rumen material from oryx that died during drought was negatively correlated with time since rainfall. Estimates of dietary crude protein derived from the protein content of rumen material were comparable to those predicted for available grass forage. The results are discussed in the context of the food and water requirements of oryx. It is suggested that during drought some grasses continue to be a source of adequate crude protein and water and of sufficient digestibility but that levels are close to minimum maintenance requirements. This and the decreasing biomass of available forage of sufficient quality lead to condition loss and death, particularly of the most vulnerable animals. Crude protein may become limiting sooner than does water.

The return of the Arabian oryx Oryx leucoryx to Oman symbolized the success of a new approach to species conservation and established reintroduction as a conservation tool. Ten years after the species had been exterminated in the wild by poaching, the first 10 founder oryx, descendants of the ′World Herd′, were reintroduced to the desert in central Oman in January 1982. A second release followed in 1984 and the population grew slowly through a 3-year drought that was broken by rain in June 1986. Further years of good rainfall and more founders meant that by April 1990 there were over 100 oryx in the wild, independent of supplementary feed and water, and using a range of over 11,000 sq km. At that time a new monitoring programme was implemented that allowed the transition from individual- to population-based monitoring and management. The population continued to grow and by October 1995 numbered approximately 280 in the wild (of which 22 were surviving founders) and used over 16,000 sq km of the Arabian Oryx Sanctuary. However, in February 1996 poaching resumed and oryx were captured for sale as live animals outside the country. Despite the poaching the population continued to increase and by October 1996 was estimated to be just over 400. However, poaching intensified and continued through late 1996 and 1997. By September 1998 it had reduced the wild population to an estimated 138 animals, of which just 28 were females. The wild population was no longer considered viable and action was taken to rescue some of the remaining animals from the wild to form a captive herd.

In this study we investigated the effect of rainfall on the home range (calculated over 90 days) of adult female Arabian oryx (Oryx leucoryx) in a reintroduced population in central Oman. We looked at response to rainfall for six rain events in the period June 1986 to January 1992; rainfall was localized on five occasions and on one occasion covered the study area. Response, in terms of range and core area, showed considerable variation between rainfall events, perhaps as a result of variation in ranging behaviour between individual oryx. However, in the first 90 days after localized rainfall the home range and core area of oryx outside rain areas increased before decreasing significantly 91–180 days after rain. In comparison, range and core area of oryx inside areas of localized rainfall either did not change or decreased after rainfall as animals took advantage of improved conditions locally rather than investigating grazing elsewhere. When rain fell over the whole study area, range size did not change, but there was an immediate increase in core area and a reduction in range overlap indicating movement to new areas. During extended drought very localized rainfall caused oryx to move quickly to areas of new rain and by 28 days 70% of all adult females had found fresh grazing. Thereafter numbers declined to around 30% by 225 days, before oryx again moved back into the new rain areas. We attributed this pattern of movement to changes in the nutritional quality, measured as crude protein, of available forage. Data for single animals revealed considerable individual variation in response to rainfall; some animals moved quickly to rain whilst others failed to reach it. This variation had consequences for reproductive success and survival and illustrated that, for the oryx, response to rainfall is a key to desert success.