MACDOUGALL-SHACKLETON, S A*; HERNANDEZ, A M; VALYEAR, K F; CLARK, A P; Univ. of Western Ontario; Univ. of Toronto; Univ. of Western Ontario; McMaster Univ.: Photostimulation induces rapid growth of song-control brain regions in male and female chickadees (Poecile atricapilla)

We explored the effects of photoperiod and sex on the song-control regions of the brain in black-capped chickadees (Poecile atricapilla). Chickadees learn both their fee-bee song as well as some calls such as the chick-a-dee. Although the fee-bee song is produced predominately by males during the breeding season, chick-a-dee calls are produced by both sexes year-round. We held male and female black-capped chickadees under one of three photoperiod treatments. Photorefractory birds were held on long days (LD) for several months and had fully regressed gonads. Photosensitive birds were held on short days (SD) for several months and had small gonads. Photostimulated birds were transferred to LD for 16 days following several months of SD and developed enlarged gonads. Following these photoperiod treatments we determined the Nissl-defined volume of the song-control nuclei HVc, Area X and the robust nucleus of the archistriatum (RA). There were significant sex differences in HVc and Area X volume, but not in RA. There were also significant photoperiod effects in HVc and Area X volume, but not in RA. In both males and females 16 days of LD were sufficient to increase the absolute volume of HVc by about 45%. These results corroborate earlier studies that indicated large-scale changes in HVc volume are rapid. As well, these results indicate that rapid growth of HVc is not dependent on exogenous hormone treatment. The large sex and seasonal differences in HVc in a species in which both males and females produce learned calls year-round also suggest that the neural substrate for production of the learned chick-a-dee call may lie outside of the song-control system.