Water Influx and Food Consumption of Free-living Oryxes (oryx Leucoryx) in the Arabian Desert in Summer

We measured water-influx rate during the hot summer in free-ranging adult Arabian oryxes (Oryx leucoryx) in Mahazat as-Sayd, a 2,244-km2 protected area in west-central Saudi Arabia. Oryxes obtained 2,294 ml/day of water in their food and from oxidative water, the latter amounting to 14.2% of total water influx. For ungulates living in hot environments, we constructed an allometric curve: log(water-influx rate [liters/day]) 5 20.885 1 0.922·log(body mass [kg]), (r2 5 0.77, F 5 26.8, P , 0.001, n 5 10). The Arabian oryx had the lowest mass-specific water-influx rate (31.5 ml kg20.922 day21), only 32% that of the camel (99.3 ml kg20.922 day21), emphasizing the degree of evolutionary specialization in oryx. Between June and September, oryxes grazed primarily on 3 grasses, Panicum turgidum, Lasiurus scindicus, and Stipagrostis. P. turgidum, taken in largest quantity, had the highest moisture content, 35–45% per g of wet matter. Dry matter intake averaged about 3.1 kg during the summer months; plant intake varied inversely with moisture content.