Structurally complex habitat and sensory adaptations mediate the behavioural responses of a desert rodent to an indirect cue for increased predation risk

We studied the foraging behaviour of a rocky desert rodent, the common spiny mouse (Acomys cahirinus), to gain insight into how structural complexity of habitat influences responses to an indirect cue for the level of predation risk. We used artificial food patches to compare the foraging response of free-ranging common spiny mice in a habitat gradient, which varied in structural complexity, between dark and moonlit nights. Close proximity to continuous overhead cover was critical to the choice of foraging microhabitat in common spiny mice, and habitat structure had a stronger effect than moon phase in the evaluation of a foraging patch, consistent with results for sandy desert rodents. The structurally complex habitat of the rocky desert environment enabled spiny mice to restrict most of their foraging to large continuous areas that offered reduced levels of predation risk. When spiny mice did forage in the open, their response can be explained by the different types of movement involved in two aspects of foraging. The number of artificial food patches visited, which reflects active and high-risk movement across open ground, was curtailed on moonlit nights. However, spiny mice reduced the food density of the most distant open food patches to similar levels, and even slightly lower ones, on moonlit compared with moonless nights. Possible explanations include the level of risk engendered by the type of movement that foraging in a tray entails combined with habitat structure (specifically camouflage afforded by shadows cast by rocks), energetic compensation for risk endured to reach the tray, and the importance of vision in anti-predator strategies in this species. This first comprehensive study of a rodent living in a rocky desert habitat demonstrates the importance of structural complexity of habitat and sensory adaptations in mediating prey behaviour under predation risk.