Benefits of small-sized caches for scatter-hoarding rodents: Influence of cache size, depth, and soil moisture

Some granivorous rodents scatter hoard; they bury seeds in shallow pits throughout their territory. These buried caches can represent food stores for the hoarders, food for competitors, or a means of seed dispersal and propagation for plants. Large numbers of seeds may be buried in many caches throughout an area; thus, fate of caches has important consequences for granivores, other animals, and plants. This study examined the ability of Ord's kangaroo rat (Dipodomys ordii) to exploit artificial caches of different sizes, at 2 depths, and in substrates of differing moisture content. Kangaroo rats harvested significantly more caches in moist substrates and at shallower depths; however, small caches containing <= 5 seeds were removed infrequently by individuals regardless of substrate moisture and depth. As cache size was increased in moist sand, a threshold existed at each depth where caches were greatly exploited by kangaroo rats. Results suggest that pilferage of caches under natural conditions is not linear with respect to cache size in moist substrates. As cache size was increased in dry sand, no threshold of increased exploitation was observed for cache sizes used in this experiment. Results also suggest that pilferage of caches under natural conditions is not strongly influenced by size in dry substrates for relatively small caches. Overall, size and depth of caches greatly influence their fate. Perturbations, such as rainfall, also alter detection of caches. To reduce detection of caches by competitors, scatter hoarders should distribute relatively small caches, especially during wet conditions.