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In a study of 52 individuals belonging to 35 species or subspecies of passerine birds it was shown that the volume of the hippocampal complex relative to brain and body size is significantly larger in species that store food than in species that do not. Retrieval of stored food relies on an accurate and long-lasting spatial memory, and hippocampal damage disrupts memory for storage sites. The results suggest, therefore, that food-storing species of passerines have an enlarged hippocampal complex as a specialization associated with the use of a specialized memory capacity. Other lifehistory variables were examined and found not to be correlated with hippocampal volume.Some species of birds store large numbers offood items, each in a separate place, and use an accurate, long-lasting spatial memory to retrieve their stores (1-5). We show here that the hippocampal complex (dorsomedial forebrain) (6) of foodstoring passerines is larger relative to body and brain size than that of nonstorers. Thus, across a range of species, a relationship has been found between the structure of a specific brain area outside sensory and motor areas and a specific behavior. METHODSWe measured the volume of the hippocampal complex and striatum of52 individuals belonging to 35 species or subspecies distributed among 9 passerine families [taxonomy in this paper follows that of Sibley et al. (7) based on DNADNA hybridization]. We defined the hippocampal complex as including the closely interconnected hippocampal and parahippocampal areas (6). The evidence from both embryological and connectivity studies (8-10) suggests that these two structures as a whole are homologous to the mammalian hippocampal complex, although the homology ofthe different subdivisions is not known. The behavioral consequences of damage to the avian hippocampal complex show that it is broadly functionally equivalent to the mammalian hippocampus in playing an important role in certain memory tasks, including those involving spatial memory (11)(12)(13)(14)(15)(16)(17)(18). The avian hippocampal complex is a paired structure located adjacent to the midline of the dorsal telencephalon (19). It extends from the caudal limit of the striatum along approximately two-thirds of the caudal-rostral extent of the striatum. In coronal section it is bounded medially by the midline and ventrally by the lateral horns of the ventricle and by the septum (Fig. 1). The region defined as the hippocampus by Karten and Hodos (19) is a V-shaped structure of densely packed cells lying ventrally and medially (Fig. 1). In the parahippocampal area large and small neurons are sparsely and nonuniformly distributed. The lateral boundary of the parahippocampal area is characterized by a change in the size distribution of neurons. Medial to the boundary the distribution is bimodal with peaks at cell areas of about 20 pIm2 and 130-150 pum2, while lateral to the boundary the distribution is unimodal with a peak at about 20-30 ILm2 (Fig. 2): the boundary is often clearer in food-storers than i...

This paper describes an investigation into whether or not spring territorial behavior was limiting the breeding density of a population of Great Tits on Wytham Estate, near Oxford. The analysis of distances between neighboring nests showed that nest sites were more spaced out than would be expected from a random distribution; this indicated that interactions between the birds produced at least a local density—limiting effect. In 2 successive years, established territorial pairs were removed from a stable spring population in mixed woodland. The removed birds were rapidly replaced by new pairs. These newcomers were largely first—year birds; they came from territories in the hedgerows that surrounded the wood; the vacated hedgerow territories were not refilled. The hedgerows were found to be suboptimal in terms of reproductive success. Thus territory limited the breeding density in the optimal habitat. Song advertisement is probably important in maintaining territorial boundaries, hedgerow birds being able to detect the presence of individual woodland territory holders by recognizing their songs. The effect of winter food supply on the population was investigated by supplying excess food throughout one winter. This artificial food supplement appeared to have no effect on the number of Great Tits breeding in the wood, but did produce an increase in the case of a related species, the Blue Tit. The results show that territorial behavior influences density; this is not considered to be a function of territory in the evolutionary sense, but rather a consequence of spacing out that has been selected for in some other context. A possible advantage of spacing out in the Great Tit is as a defense against predators. Territory size varies considerably from year to year. These variations are the result of interactions between the birds themselves, rather than direct adjustments of territory size to fluctuations in some environmental resource. Even though territory has an effect on the number of birds breeding in the wood,it is not an important density—dependent factor acting to regulate the population.