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.