Extirpated from the wild in 1972 by overhunting, Arabian oryx (Oryx leucoryx) were re-introduced in Saudi Arabia in March 1990; 17 oryx were released into Mahazat as-Sayd, a 2244 km 2 fenced reserve in westcentral Arabia, which lies at the periphery of their historical home range. The population has increased to 346 animals. The National Commission for Wildlife Conservation and Development, and those that manage the herd, have recently asked, 'What is the optimal management strategy to assure long-term persistence of the species, given the absence of immigration and predation?' Food resources, determinants of rates of mortality and birth, covary with unpredictable rainfall in Mahazat as-Sayd. Using data-driven assumptions, we developed a computer model that evaluated the probability of extinction (P ex ) under various management strategies: no intervention, removing a fixed number of animals each year, removing a fixed percentage of animals each year, and removing all individuals above a threshold. In addition, we explored the probability that oryx populations would decline below two thresholds, called the probability of quasi-extinction (P q-ex ) under various management schemes. Our analyses suggested that, without intervention, the oryx population had a high P ex . Removing 15% of the current population provided a low P ex , but this method also produced high values for P q-ex and, as a by-product, wide fluctuations in population size (N). Although it required an assessment of both N and carrying capacity (K), the most successful management plan consisted of removing all oryx above 70% of K. Adoption of this plan resulted in low P ex, low P q-ex , and smaller fluctuations in N. Our study may provide a useful model for evaluating management plans for a variety of threatened animal populations in desert ecosystems.

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 Arabian oryx inhabits an environment where summer ambient temperatures can exceed 40°C for extended periods of time. While the oryx employs a suite of adaptations that aid survival, the effects of this extreme environment on inactivity/sleep, where ambient temperatures often exceed mammalian thermoneutral zones, are unknown.To determine how the oryx manages inactivity/sleep seasonally we used fine and coarsegrain actigraphy, in 16 animals, to reveal when the animals were inactive/sleeping in relation to variations in ambient temperatures and light levels. We demonstrate that during the cooler winter months the oryx is inactive/sleeping during the cooler parts of day (pre-dawn hours), showing a diurnal activity pattern. In contrast, in the summer months, the oryx displayed a crepuscular activity pattern, with the major inactivity/sleep bouts occurring equally during both the coolest part of the night (pre-dawn hours) and the hottest part of the day (afternoon hours). Interestingly, the daily rhythm of the timing of changes in core body temperature did not vary seasonally, although the amplitude did change. The transition from winter diurnal activity to summer crepuscular activity occurred in May, while the reverse occurred in September. By having half of the major summer sleep bouts during the hottest part of the day, the oryx may take advantage of the thermoregulatory physiology of sleep to mitigate increases in body temperature. The seasonal summer desynchronization of circadian entrained daily rhythms (core body temperature and daily activity patterns) is suggestive of temperature acting to mask, or modify, output pathways from the suprachiasmatic nucleus.

Post-release monitoring, including abundance cision, interdependence of consecutive estimates, and the assumption that all gains and losses are recorded,

The spatial distributions of 20 female and 15 the western part of the protected area and around the Camp could potentially reduce the eCective carrying male Arabian oryx Oryx leucoryx, reintroduced into the fenced Mahazat as-Sayd protected area (2,244 km2) in capacity of the reserve, change the social structure of the population, facilitate the transmission of disease, modify western Saudi Arabia between 1990 and 1994, were examined from their release until the end of 1999. Over habitat in the form of a piosphere (a zone of attenuating animal impact away from a watering point) around this period we observed a westward shift in home range location of most male and female founder oryx to the Camp, and reduce potential genetic flow within the reintroduced population. Whereas wild-born oryx were include the Rangers' Camp within core areas of activity, despite rain falling in patches throughout most of the observed at the Camp, founders were disproportionately represented, suggesting that potential problems associated reserve. Sporadic and unplanned availability of water had occurred at the Camp during several years. The with dependence on the Camp may diminish as the total population increases and ages. 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 Keywords Arabian oryx, home range, Oryx leucoryx, reintroduction, Saudi Arabia, spatial distribution, water Camp tended to be older individuals and those released in the first years (1990-1992). Concentration of oryx in availability. independent of drinking water (Tear et al., 1997; Williams