Patch use, apprehension, and vigilance behavior of Nubian Ibex under perceived risk of predation

Foraging theory predicts that animals will sacrifice feeding effort in order to reduce predation risk. Once a forager chooses a habitat, it must decide how to allocate its foraging effort. Nubian Ibex are diurnal, social, cliff-dwelling herbivores. Many of their characteristics seem to have evolved as responses to predation risk. In order to assess the effects that perceived risk of predation might have on foraging behavior of free-ranging Nubian Ibex in the Negev Desert, Israel, we measured giving-up densities (GUDs) in artificial food patches and used them to gauge apprehension level. (Apprehension can be defined as a reduction in attention devoted to performing an activity as a consequence of reallocating attention to detecting or responding to predation risk. A forager can also be vigilant. Vigilance is often defined as time spent scanning the surroundings with the head up.) We also quantified time budgeting using focal observation of individual Nubian Ibex. Habitat preferences and patch selectivity as a measure of apprehension were considered. In particular, we tested the effect of distance from refuge on GUDs, the effect of micropatch structure on selectivity, and the effect of distance from the refuge and group size on Nubian Ibex vigilance level and apprehension. Nubian Ibex allocate their foraging effort more toward patches closer to the escape terrain. At the same time, Nubian Ibex are more apprehensive at intermediate distances from the cliff edge than nearer the cliff, and their use of vigilance increases with distance from the cliff edge. These results suggest that Nubian Ibex may switch from apprehension to a more extreme behavior of vigilance at greater distances from the refuge. This study demonstrated the use of antipredatory behaviors, apprehension, and vigilance by a forager. Estimating apprehension and vigilance levels of a forager simultaneously gives a more complete and accurate picture of how the habitat is perceived by them and combined with measurements of GUD allow a more accurate assessment of habitat quality. Copyright 2007, Oxford University Press.