Clark's nutcracker spatial memory: many errors might not be due to forgetting

Abstract

Clark's nutcrackers,Nucifraga columbianarely upon cached seeds for both winter survival and breeding. Laboratory studies have confirmed that nutcrackers use spatial memory to recover their caches. In the laboratory, however, nutcrackers seem to perform less accurately than they do in nature. Two lines of evidence indicate that nutcrackers make ‘errors’ in the laboratory that are not due to failures of memory. First, when digging in sand-filled cups, nutcrackers were 89% accurate when they plunged their bills directly into the middle of cups but only 21% accurate when they swept their bills across the cups. Second, nutcrackers were more accurate when the cost of probing was increased by covering sand-filled cups with either petri dishes or heavy glass bowls. Birds recovered caches in order of increasing costs. As costs increased, nutcrackers made somewhat fewer errors nearer to cache sites before recovering the caches and dramatically fewer errors further away from cache sites or near cache sites after recovering the caches. Some errors may be a form of environmental sampling. We conclude that the impressive achievements documented by previous studies are underestimates of the spatial memory abilities of Clark’s nutcrackers.