Three families of North American passerines--chickadees, nuthatches and jays--store food. Previous research has shown that memory for the spatial locations of caches is the principal mechanism of cache recovery. It has also been previously shown that the hippocampal complex (hippocampus and area parahippocampalis) plays an important role in memory for cache sites. The present study determined the volume of the hippocampal complex and the telencephalon in 3 food-storing families and in 10 non-food-storing families and subfamilies of passerines. The hippocampal complex is larger in food-storing birds than in non-food-storing birds. This difference is greater than expected from allometric relations among the hippocampal complex, telencephalon and body weight. Food-storing families are not more closely related to each other than they are to non-food-storing families and subfamilies, and the greater size of the hippocampal complex in food-storing birds is therefore the result of evolutionary convergence. Natural selection has led to a larger hippocampal complex in birds that rely on memory to recover spatially dispersed food caches.