Visual environment and delay affect cache retrieval accuracy in a food-storing rodent

Many scatter-hoarding species use spatial memory to relocate their food cac hes. Two factors can affect spatial memory: the availability of landmarks i n the environment, and the latency between learning and recall. Using a 2 x 2 factorial design, we determined the effect of these factors on cache ret rieval accuracy in Merriam's kangaroo rats (Dipodomys merriami). Kangaroo r ats cached seeds in an arena under conditions that varied by retrieval inte rval (1 or 10 days) and by number of landmarks (0 or 16 landmarks). After 1 day, they recovered equal proportions of caches in both landmark condition s. After 10 days, they recovered more caches in the 16-landmark condition t han in the bare condition. This is the first study to show that landmarks a re necessary for accurate cache recovery after long delays. This result is consistent with maze studies that have shown that landmarks reduce proactiv e interference and that delay increases proactive interference.