Landmarks, the Hippocampus, and Spatial Search in Food-Storing Birds
Food-storing birds use global landmarks to relocate their caches and make relatively little use of local landmarks that pinpoint the locations of caches. Experiments with black-capped chickadees showed that removal of local landmarks was without effect on search accuracy, whereas removal of global landmarks reduced search accuracy. When global landmarks were rotated, birds searched in sites that were correct with respect to the rotated landmarks. In separate experiments it was found that bilateral hippocampal lesions disrupted the accuracy of search for caches without affecting the intensity of search. Birds with hippocampal lesions also showed a deficit in memory for well-learned spatial locations, although memory for cues associated with food was intact. Hippocampal lesions led to large numbers of working memory errors, however, on both spatial and nonspatial tasks. These results show that to relocate their caches black-capped chickadees use stimuli more complex than cues directly associated with cache sites. Comparative studies showed the hippocampal complex to be larger in food-storing birds than in other species. This increase in size of the hippocampal complex occurs convergently in three families of food-storing birds and is probably an adaptation to the cognitive demands of creating and retrieving scattered caches of food.