DEVELOPMENT OF HIPPOCAMPAL SPECIALIZATION IN 2 SPECIES OF TIT (PARUS SPP)

Food storing birds have been shown to have a larger hippocampus, relat ive to the rest of the telencephalon, than do non-storers. A previous study reported that this difference in relative hippocampal volume is not apparent in a comparison of nestling birds, but emerges after bird s have fledged. This conclusion was based on a comparison of a storing and a non-storing species in the corvid family. The present study com pared another storer/non-storer pair of species in order to test wheth er the results of the previous study can be replicated in another fami ly of birds. The volumes,of the hippocampal region and remainder of th e telencephalon were measured and estimates of neuron size, density an d total number in the hippocampal region were made for nestlings and a dults of the food-storing marsh tit Parus palustris and non-storing bl ue tit Parus caeruleus. Relative hippocampal volume did not differ bet ween nestlings of the two species, whilst the relative hippocampal vol ume of adult marsh tits was greater than that of blue tits. The differ ence between adults arose because in marsh tits but not blue tits, adu lts had a significantly larger relative hippocampal Volume than did ne stlings. Neuron density was significantly higher in both species in ne stlings than in adults and adult blue tits had fewer neurons than did adult marsh tits. The results of this study are largely consistent wit h the earlier study comparing a storing and non-storing species of cor vid, suggesting that the observed patterns may reflect a general diffe rence between storers and non-storers in the development of the hippoc ampal region.