Scatter hoarding by kangaroo rats (Dipodomys merriami) and pilferage from their caches

Abstract

We observed radio-implanted Merriam's kangaroo rats disposing of 10-g bonanzas of rolled oats in 48 trials in the field. The principal determinant of the initial disposition of discovered food was apparently its distance from the day burrow: food found within about 10m was mainly larder hoarded, whereas food encountered farther afield was usually dispersed immediately in shallow caches. Cache sites were newly dug for the purpose and not reused; most caches were nearer the current day burrow than was the food source, but a few were placed far from both the cacher's day burrow and its habitual nocturnal range. An experiment with artificial caches indicated that security from discovery increases with spacing and with proximity to perennial shrubs. Nine kangaroo rats cached dyed food, and fecal dye traces revealed extensive pilferage from five of them, by both conspecifics and other rodent species. Limited evidence indicates that food encountered nearer home and initially larder hoarded was more secure from pilferage than food initially scattered, and yet kangaroo rats were observed to scatter caches soon after initial larder hoarding. A kangaroo rat whose dyed stores escaped pilferage fed from them at intervals for at least 12 days. Even cachers who incurred pilferage made as much, or more, use of their caches as any thief, suggesting that scattering caches may be a defense against catastrophic losses.