ABSTRACT
Clark's nutcrackers regularly store large numbers of pine seeds and remember the locations of the cached seeds. Although they are very accurate, they do make some errors during recovery. In an attempt to determine whether any behaviours during caching predicted the occurrence of errors during recovery, we videotaped Clark's nutcrackers while they cached and recovered seeds under laboratory conditions. We used the videotapes to develop complete, quantitative descriptions of caching and recovery behaviour, with an emphasis on body orientation and directions of movement. During caching, the birds showed the greatest change in their orientation and direction following cache creation. During cache recovery, in contrast, body orientation changed most following successful recovery of a seed. When orientation while making a cache was compared with orientation when recovering the same cache, orientations were similar more often than would be expected by chance. However, this consistency of direction was not related to the accuracy of cache recovery, indicating that such consistency is not necessary for accurate cache recovery. The location in which the birds chose to place their caches was the only variable that predicted the location of probes during recovery. Copyright 1999 The Association for the Study of Animal Behaviour.
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.1997The Association for the Study of Animal Behaviour
