Fig. 1.

A: Phylogenetic relationships of living birds (Sibley and Ahlquist, 1990) with vocal learners highlighted in red, possible independent gains of vocal learning highlighted with red dots, or possible independent losses highlighted with green dots. B: Semi-3D view of seven cerebral vocal regions (yellow and red) found in each of the vocal learning bird groups and of auditory regions (blue) found in all birds. The three red-labeled vocal nuclei in the cerebrums are in nearly identical locations in all three vocal learning orders, and in songbirds constitute what is called the anterior vocal pathway. The four yellow-labeled cerebral vocal nuclei are in different locations across vocal learning orders, but in the same brain subdivisions relative to each other, and in songbirds constitute what is called the posterior vocal pathway. The posterior RA-like nucleus (hummingbird VA and parrot AAC) projects to the brainstem motor neurons (nXIIts) that control the syringeal muscles for production of sounds (Nottebohm et al., 1976; Paton et al., 1981; Striedter, 1994; Durand et al., 1997; Gahr, 2000). See Figure 4A,B for neural connectivity in songbirds. (Modified from Jarvis et al., 2000.) Scale bars = 1 mm.