The effect of vegetation cover on vigilance and foraging tactics in the fat sand rat Psammomys obesus

The combination of the visual obstruction and protection properties of vege tation is considered to be one of the most important factors determining th e trade-off between vigilance and foraging in a prey species. In the Negev desert, diurnal fat sand rats construct their burrows in the ephemeral rive r beds ("wadis"), under dense and tall shrubs of Atriplex halimus, or on th e open first fluvial terrace, covered with scattered low shrubs of Anabasis articulata. We tested the hypothesis that properties of the vegetation wou ld affect the time budget of female sand rats. Sand rats spent more time ab oveground, rested more, were less vigilant, and moved more slowly under the dense cover in the wadi than at the open terrace. No differences in the to tal foraging time were revealed, but foraging tactics varied between habita ts: individuals in the wadi mainly fed aboveground, whereas those at the te rrace mainly hoarded. Our results indicate that sand rats perceive the dens e vegetation cover as good protection despite its visual obstructive nature , and that vigilance in Psammomys obesus is performed at the cost of restin g rather than at the cost of foraging.