Figure 2. Development of song in Hylophylax naevioides.

(A) Broadband spectrograms of vocalizations produced by two captive individuals demonstrating different stages towards the production of crystallized adult song. Upper panel, a male bird reared in isolation with no tutor (NT1): subsong at 51 and 59 days post hatching (dph); incipient song at 74 dph; crystallized song at 86 dph. Lower panel, a female bird reared in isolation with a heterospecific tutor (HT1): subsong at 46 and 68 dph; incipient song at 81 dph; crystallized song at 83 dph. (B) Ages (dph) at which the five stages of song production (babbling, subsong, incipient song, crystallized song, and soft song) were produced by two male birds reared in isolation with no tutor (NT1, NT2; left of the red line) and three female birds reared in isolation with a heterospecific tutor (HT1, HT2, HT3; right of the red line), until the end of the experiment for each individual (200 dph). See methods for description of song production developmental stages.