SANFORD, K.H.*; BREUNER, C.W.; HAHN, T.P.; PRAVOSUDOV, V.V.; Univ. of California, Davis; Univ. of Texas, Austin; Univ. of California, Davis; Univ. of Reno: Relative hippocampal volume is affected by age in migratory Mountain White-Crowned Sparrows

The hippocampus (HF) is necessary for the formation of spatial memories. Migratory birds rely on spatial memory as part of their navigational system, and research suggests HF is important in migration. However, few studies have investigated the development of HF in migratory birds. Based upon research on HF of food caching birds, we hypothesized that HF in long-distance migrants is experience dependant, and that migration affects development of the avian HF. Mountain White-Crowned Sparrows (Zonotrichia leucophrys oriantha; MWCS), long distance migrants, breed in sub-alpine meadows of the northwestern US and winter in the southwest and northern Mexico. We collected 20 wild MWCS (5 juvenile males, 6 juvenile females, 5 adult males, 4 adult females) from California�s high-Sierra mountains to asses the effects of age and sex on the development of HF. All birds were caught in late summer prior to migration to insure that the juveniles were developmentally independent, but had not yet gained migratory experience. Adults were assumed to have had at least one year of migratory experience. HF and telencephalon (T) of each bird was measured, and volumes compared. We found that while gender had no effect on either brain region, juveniles had significantly larger T volumes than adults. Additionally, HF volume relative to T was larger in adults than in juveniles, which implies that T shrinks with age and HF either does not change in size or grows. While we did not see any difference in the absolute volume of HF with age, our results do suggest that even after independence is reached significant changes take place within the avian brain that may be related to migratory experience.