Influence of cover on the foraging behavior of Negev Desert gerbils

We studied the influence of cover types on the foraging behavior of two coexisting gerbils (Gerbillus pyramidum and Gerbillus andersoni allenbyi) by experimentally manipulating cover patches in an otherwise natural setting in the sandy habitats of Negev Desert, Israel. Two types of cover manipulation were carried out, “low” (10cm high) and “high” (30cm high), and these were compared to natural, thinly vegetated cover (the control). We used artificial food patches (seed trays) to record the foraging behavior of the gerbils. The gerbils showed significantly lower GUDs (giving up density: the amount of seeds remaining in a food patch following a forager’s visit) in artificial resource patches (seed trays) located in the low cover patches as compared to high cover and control patch types. This result indicates lower cost of foraging in low cover stations due to reduced predation risk. In addition, in low cover stations, the dominant species G. pyramidum had significantly lower GUDs compared to G. a. allenbyi, indicating higher foraging efficiency. In high cover stations, the gerbils had their highest GUDs, even more than control treatment, suggesting less preference for habitats where cover merely acts as an obstruction for predator detection instead of providing safety. Cover manipulation also had a significant effect on habitat quality. The numbers of gerbil burrows were significantly greater in low cover stations than the other two types, suggesting a preference for habitats in which high quality refuges (from foxes) are abundant. In addition, the gerbils showed significant differences in GUDs across moon phases in different cover types. Fox activity was significantly higher in control as compared to high and low cover stations. This was in accordance to the gerbil’s greater apprehension there as indicated by higher selectivity for “full” resources patches when compared to more-difficult-to-exploit “bottom” patches along different periods of night.