Fig. 5: Model of song development.
From: Cumulative cultural evolution and mechanisms for cultural selection in wild bird songs
We used two age classes (J = juvenile and A = adult) and three classes of introductions (C = click trains, X = high note clusters, and XC = both). In the late spring of a given year (time = t), only adult males are present. In late summer, those adults have bred and both they and juvenile males are present; at this intermediate time (ti) each male is initially allocated the same introduction type as his father (solid lines). Then, as song development progresses and juvenile males can be influenced by other tutors, they may retain their initial introduction type or switch to either of the other two types (dashed lines) before they crystallize their songs late in the following spring (time = t+1), and join the breeding cohort, which also includes adult males from the previous year who returned to breed again.
