Seedling-aided cache detection by heteromyid rodents.

Heteromyid rodents are granivores which frequently cache seeds in numerous scattered locations and use olfaction to relocate these caches. However, seedlings which emerge from these caches may also serve as cues to cache location. We conducted an experiment in the western Great Basin to determine whether heteromyids perceive emerging seedlings of Indian ricegrass, Achnatherum hymenoides, as beacons to cache locations. Specifically, we compared frequencies with which heteromyids searched for seeds among locations differing in the presence or absence of buried seeds and above-ground seedling treatments, which included either a single Indian ricegrass seedling or an artificial seedling proxy. The olfactory cue related to seeds was clearly important in relocating caches, as digging by heteromyids near artificial seedlings and at control locations lacking seedlings was significantly more likely if seeds were present. However, rodents dug for seeds near natural seedlings at similar frequencies regardless of whether a seed cache was actually present at the base of the seedling. Moreover, seeds had no effect on the frequency at which rodents exhibited investigative, superficial digging behavior near artificial seedlings. The latter results indicate that heteromyids do associate emerging seedlings with cache locations, and that this association may primarily be a beacon to potential cache locations. Seedling-aided cache detection is important because it could improve the effectiveness of cache-searching behavior during a period when recovery of caches is critical for survival.