Migratory dark-eyed juncos, Junco hyemalis, have better spatial memory and denser hippocampal neurons than nonmigratory conspecifics

The evolution of migration in an animal population produces a suite of physiological, behavioural and cognitive adaptations. Migratory birds, in particular, require the ability to return annually to breeding and wintering sites after long journeys, and thus might be predicted to have evolved enhanced spatial memory. In a comparison of two sparrow subspecies that co-occur in winter, the migratory subspecies (dark-eyed junco, Junco hyemalis hyemalis) performed better than the nonmigratory subspecies (J. h. carolinensis) on a room-scale spatial memory test. The migratory juncos also had more densely packed hippocampal neurons than did nonmigrants. Among nonmigrants, we looked for hippocampal differences between birds that occupied two home ranges annually and those that remained on their breeding territory year-round, to determine whether migration, per se, is related to neuroanatomical differences. However, we were unable to reach any conclusions because of low statistical power. A denser hippocampus could be the basis for better spatial memory in migrant juncos. Further testing of spatial memory on a landscape scale is needed to strengthen this argument and to understand cognitive differences between migrants and nonmigrants. (C) 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.