Food Hoarding by Merriam's Kangaroo Rats: A Test of Alternative Hypotheses

Abstract

Merriam's kangaroo rats (Dipodomys merriami) store seeds in burrows (larderhoarding) and in small clumps in shallow holes dug in the soil (scatterhoarding). We used a large laboratory arena with an artificial burrow for larderhoarding and four sand—filled compartments for scatterhoarding to test several alternative hypotheses about spatial patterns of food caching. The hypotheses were that kangaroo rats prefer to (1) larderhoard seeds in burrows, (2) scatterhoard seeds near burrows, (3) scatterhoard seeds away from burrows, (4) scatterhoard seeds near food sources, or (5) make widely spaced scatterhoards. Three treatments that differed in the distance between the burrow and food source were used to discriminate among hypotheses (2) through (4). There was a substantial amount of variation among individuals in proportion of seeds that were larderhoarded. Subjects initially scatterhoarded seeds close to the food source, but distributed caches more evenly among caching compartments as trials progressed. Increased evenness of cache distribution resulted from harvesting and repositioning of extant caches as well as selective placement of new caches. Initial caching close to food may be adaptive by maximizing harvest rates during flushes of seed production and making seeds unavailable to non—digging competitors (birds and ants). Subsequent redistribution of caches may make them less available to other rodents that locate buried seeds by smell and use area—restricted search to find closely spaced scatterhoards.