Tactile discriminatory ability and foraging strategies in Kangaroo rats and pocket mice (Rodentia: Heteromyidae).

A comparative study of seasonal food hoarding activity and tactile discriminatory ability in four species of heteromyid rodents (Dipodomys panamintinus, D. merriami, Perognathus longimembris, and P. formosus) was conducted in laboratory test arenas. Animals were tested individually to determine their treatment of seed (white millet) and seed mimics (glass beads and gravel) offered as food. In general, all animals showed low levels of millet hoarding activity during winter months with higher levels in fall and spring. Observations revealed that all species manipulated (with the forepaws) each potential food item prior to eating, pouching, or rejecting it. These tactile cues appear to surpass visual and olfactory cues as critical factors in distinguishing between food and food mimics. Pocket mice (Perognathus) showed high levels of tactile discriminatory ability which may serve as the mechanism by which they achieve high foraging efficiency in nature when "filter-feeding" for widely dispersed seed resources. Kangaroo rats (Dipodomys), on the other hand, are less adept at distinguishing between food and very similar non-food items. The fact that, in nature, kangaroo rats depend heavily on clumped food resources may obviate the need for highly efficient tactile discriminatory abilities.