Neuroendocrine Modulation of Coordinated Acoustic Signals

Coordinated acoustic displays, in which two or more individuals combine their sounds to produce collaborative signals, are among the most remarkable and least understood forms of animal communication. While many studies have focused on the evolution and potential functions of coordinated displays, especially the male–female duets of many songbird species, relatively little is known about the underlying neural and hormonal bases of acoustic coordination. Here, we use our current understanding of the neuroendocrine mechanisms involved in signal perception and production—with a focus on songbirds—to explore the roles that these mechanisms might play in coordinated acoustic displays. Recent research suggests that brain regions of the song control system play important roles in processing salient social cues during signal coordination to correctly modulate the timing of appropriate motor responses by signaling partners. These regions associated with signal coordination are particularly sensitive to steroid hormones in songbirds and other taxa that display coordinated acoustic behaviors. In this chapter, we focus on estrogens and androgens—the two “sex” steroids that play an oversized role in communicative behavior in birds. Decades of research suggests that these steroid hormones regulate the development and modulate the activity of brain regions important for vocal and non-vocal coordinated sonations. However, our understanding of these systems has been limited by a disproportionate research focus on male brains and relatively few previous studies of female brains and behavior. We discuss what we have yet to understand, and we offer some potential avenues for future research.