Landscape-Scale Foraging Decisions by Reintroduced Arabian Oryx

Abstract

We evaluated landscape-level movements of reintroduced Arabian oryx (Oryx leucoryx) in relation to rainfall for 8 years (1982-89). For the first 4 years (1982-85), captive-bred oryx released into habitat devoid of conspecifics demonstrated a distinct shift in movement patterns as foraging conditions deteriorated. Based on mean monthly estimates, during the first 2 months after rain, oryx used large areas (297-724 km 2 ), exhibited low site fidelity (15-32%) overlap between consecutive months), high range expansion (45-62%) new area used each month), and undertook more long distance journeys than expected (P < 0.01). From 2 to 3 months after rainfall, oryx reduced the amount of area used by 86%, increased site fidelity by 72%, reduced range expansion by 29%, and gradually suspended long distance forays. We related this shift to the low nutritive quality of the oryx's primary forage species (Stipagrostis spp.). Once Stipagrostis declined to extremely low levels of crude protein, copper, and phosphorus, the oryx apparently suspended their nutritionally costly searching activities, and instead remained in areas where Stipagrostis was most palatable. In contrast, in years 6 through 8 following their release, the oryx responded to rain with no apparent shift in foraging patterns. Instead, they exhibited less variable and reduced levels of range expansion (10-42%) and area use (180-211 km 2 ). In addition, site fidelity was more consistent on a monthly basis (46-65% overlap),. and long distance movements were more random regardless of the influence of rainfall on the nutritive value or palatability of Stipagrostis. The changes in movement patterns over time were attributed to: (1) a reduction in the oryx's threshold of acceptance for low-quality Stipagrostis; (2) decreased consumption of Stipagrostis and a concomitant increase in browse consumption, and (3) greater knowledge of the landscape. Captive-bred oryx released in years 7 and 8 into the existing reintroduced population reacted to changes in forage nutritive quality caused by rain with a similar shift in foraging patterns as exhibited by the first releases during their first 4 years in the desert. This result emphasizes the relative importance of learned foraging behavior in explaining changes over time in the movement patterns of the oryx. Results of this study indicate that reintroductions of social herbivores should be implemented in ways that enhance the transfer of knowledge from experienced to naive individuals.