EFFECTS OF SUBSTRATE ON FORAGING DECISIONS BY A NAMIB DESERT GERBIL

We investigated the role of foraging and escape substrates on foraging decisions of a Namib Desert gerbil, Gerbillurus tytonis (Rodentia), i n the field. We used the giving-up density technique, which uses artif icial seed trays to assess foraging decisions. We tested whether the f oraging decisions made in the trays were an artifact of prior knowledg e of a food source by comparing giving-up densities in trays that were randomly placed in different parts each night with that in trays that remained in fixed position throughout the experiment. There was no si gnificant difference in giving-up densities between these two treatmen ts, which suggests that prior knowledge of food location does not affe ct foraging decisions. We examined the preferences of gerbils for the different substrates using seed trays. The gerbils showed significant differences among habitats in the amount of seed taken and between new -moon and full-moon nights. They removed more seeds where the differen ce between the size of the seeds and the size of the sand substrate wa s large. This finding is congruent with the hypothesis that tactile di scriminatory ability affects the foraging behavior of these rodents. A lthough these rodents alter their foraging behavior in response to pre dation risk, there was no significant difference in the amount of seed s taken in habitats differing only in the degree of compaction of esca pe substrates.