The number of new neuronal and non-neuronal cells co-vary significantly within, but not across, cohorts (also see Table 4). The results of Spearman’s rank correlation from comparisons of: (A) neuronal and non-neuronal cells labeled with the first thymidine analog in SD, (B) neuronal and non-neuronal cells labeled with the second TA in SD, (C) neuronal and non-neuronal cells labeled with the first thymidine analog in LDT, (D) neuronal and non-neuronal cells labeled with the second thymidine analog in LDT. The correlation between new neuronal and non-neuronal cells within, but not across, thymidine analog-labeled cohorts suggests that a temporally controlled common factor present during both breeding and nonbreeding conditions mediates addition, survival, or both of new cell populations.