Background

Just as human infants learn to produce complex speech sounds from adults, young songbirds learn to produce complex vocalizations (i.e., song) from adult tutors during a critical period of development. Because general animal models in life science research, such as mice and monkeys, do not exhibit vocal learning, songbirds offer a great opportunity to study neural substrates of vocal learning, an essential element of human speech acquisition (Doupe and Kuhl, 1999; Bolhuis et al., 2010). Moreover, birdsong learning critically depends on a basal ganglia-thalamo-cortical circuit that is discrete and specialized for this single task. This circuitry contrasts sharply with homologous mammalian circuits. Thus, songbirds are considered a tractable model system for studying neural mechanisms underlying basal ganglia-dependent motor skill learning (Doupe et al., 2005).

In the zebra finch, the most popular songbird species used for neurobiological study of birdsong learning, adult male birds sing in two social contexts: singing toward females in a courtship context (directed singing) and singing alone in a solo context (undirected singing). A large body of evidence suggests that undirected singing is a state of vocal practice in which birds improve and optimize song structure, whereas directed singing is a state of motor performance in which birds exploit what they have already learned to impress a female (Jarvis et al., 1998; Kao et al., 2005 and 2008; Kojima and Doupe, 2011; Kojima et al., 2018). Thus, comparing song structure and neural activity between the two social contexts is a standard and important approach to examine behavioral and neural mechanisms of song learning. In contrast with recordings of undirected song, which a male bird produces in isolation, recordings of directed songs are often contaminated by vocalizations of a female bird presented to elicit directed song. Female birds often produce loud calls while the male is singing, and their calls often overlap with male songs. Such contamination with female calls can cause serious deterioration of data quality and in many cases, results in exclusion of song data from analyses. To avoid such contamination, we developed a relatively easy surgical procedure to devocalize female birds almost permanently.

Several previous studies have reported surgical procedures to devocalize birds, but they are either technically difficult (Cooper and Goller, 2004) or unsuitable for long-term devocalization (Pytte and Suthers, 1999). The current protocol describes a novel method for devocalizing female zebra finches using tubing inserted into the bronchi to prevent adduction of the lateral labia into the expiratory air stream that is responsible for phonation (Goller and Larsen, 1997; Larsen and Goller, 2002). This method enables us to devocalize birds almost permanently without great technical difficulties. Because this devocalization protocol can be applied to males as well as females, it can be used in both sexes for investigating the role of vocalizations in social communication, including courtship behavior and social bonding.