A volumetric comparison of brains between greylag geese (Anser anser L.) and domestic geese.

Volumes of brain and brain subdivisions in greylag and domestic geese are determined by cytoarchitectonical methods in order to confirm the reduction in brain weight of 16.13% due to domestication which was described in an earlier study. Olfactory structures, nucleus basalis and the 'piriform' corticoid layer are found to be particular different in shape and position compared to other birds, especially the pigeon. The volumes of brain parts in relation to the total brain are very similar in both: greylag geese and domestic geese. The extent of changes in brain parts due to domestication varies. The decrease of the prosencephalon by 18.8% is double the size of the rhombencephalon (9%). Remarkable are the reduction values of the tectum opticum (21.8%), the tractus opticus (37.3%), the hyperstriatum ventrale (26.1%), the archistriatum (22.4%), and the hippocampus (31%). Changes in brain size are compared with observations found in other domesticated birds. Evolutional, functional and environmental connexions are discussed as well.