Placement and recovery of seed caches by a solitary rodent, Ord's kangaroo rat (Dipodomys ordii)

Abstract

Seed caching is a common behavior that has important ecological consequences for seed-hoarding animals, granivorous competitors, and plants whose seeds are harvested and stored. Despite the significance of this behavior, patterns of storage and recovery of caches for many food-hoarding animals in the wild remain poorly understood. For example, many rodents are prolific and dynamic seed hoarders, storing large quantities of seeds in larderhoards (repeated deposits of seeds in a centralized location) and scatterhoards (small, scattered, subsurface caches), yet few factors that influence placement of caches by rodents have been identified. Furthermore, no study has examined seasonal shifts in placement of caches by seed-storing animals that forage throughout the year. Preliminary investigations revealed that Ord’s kangaroo rats (Dipodomys ordii) are active year-round in the Sandhill Region of Nebraska and that these rodents deposit seeds of soapweed yucca (Yucca glauca) in both larderhoards and scatterhoards. This unique situation provided an opportunity to investigate use of burrows, seed-caching patterns, and recovery of caches by a solitary rodent in the wild. Ord’s kangaroo rats inhabited burrows alone and typically used multiple burrows in summer, but only 1 burrow in winter. Additionally, individuals took yucca seeds directly to burrows in winter (larderhoarding), but distributed seeds into shallowly buried caches in summer (scatterhoarding). Kangaroo rats likely larderhoarded seeds in winter to have convenient access to resources and because few suitable sites were available to scatterhoard seeds in this season. In summer, kangaroo rats placed caches in a clumped arrangement closer to seed sources than to burrows, following the rapid-sequestering hypothesis. In a test of recovery of caches, kangaroo rats did not have a distinct advantage over pilferers in recovering their own scatterhoards of yucca seeds. Although seed caches were recovered quickly, most caches were only partially recovered. Finally, burrows of Ord’s kangaroo rats were simple in structure and contained few seeds in summer; reinforcing the observation that larderhoarding was uncommon in this population in summer. Overall, evidence indicates that Ord’s kangaroo rats are flexible seed hoarders as they switch patterns of seed storage and use of burrows seasonally. Furthermore, their storage and incomplete recovery of caches has important implications for dispersal of plants in the Sandhill Region.