Long-term spatial memory in clark's nutcracker, Nucifraga columbiana

Clark's nutcrackers, Nucifraga columbiana, are known to depend on cached seeds as their major food source throughout the winter and spring at high elevations; they use spatial memory to locate their hidden seed caches. Field observations of caching in the autumn and recovery in the spring suggest that memory for cache sites may last as long as 7-9 months. Twenty-five Clark's nutcrackers were tested for their ability to remember the location of their caches after intervals of 11, 82, 183 and 285 days. Birds were allowed to make between 18 and 25 discrete caches in a room containing 69 randomly selected sites. After caching, the birds were randomly assigned to one of four retention intervals. Each bird was given three recovery sessions. When the number of caches recovered was compared with the number expected if the birds probed randomly, performance was significantly above chance during each recovery session. There were no significant differences among the groups in percentage of correct probes. There was, however, a significant increase in errors across the three recovery sessions. Birds assigned to the retention interval of 285 days made many more errors during the last recovery session and also took longer to find caches than birds with shorter retention intervals. Although Clark's nutcrackers can remember the locations of cache sites after 285 days, some forgetting appears to occur between 183 and 285 days.