Fig. 7.
The volume encompassed by single arbors (inmm3; top panel) and the proportion of lMAN occupied by DLM arbors (bottom panel); means ± SEM. The volume encompassed by DLMDL arbors increased between 20 and 35 d and then decreased between 35 d and adulthood, although these changes were not significant. However, the proportion of lMANcoreoccupied by individual arbors increased between 20 and 35 d followed by a slight decrease between 35 d and adulthood. The volume encompassed by DLMVM arbors decreased significantly between 20 d and adulthood. The decrease in this measure, accompanied by the dramatic increase in overall volume of lMANshell between 20 and 35 d, produced a significant decrease in the proportion of lMANshell occupied by single arbors, suggesting that the degree of overlap between DLMVMarbors decreases substantially during the sensitive period for song learning. There was no significant change in the proportion of lMANshell occupied by DLMVM arbors between 35 d and adulthood.