Canary song syntax moves between order and disorder

Many complex behaviors involve sequences of basic motor or vocal elements governed by syntactic rules, which facilitate flexible and adaptive actions. Songbirds that crystallize their repertoire of vocal syllables and syllable-to-syllable transitions allow researchers to build probabilistic models of syntax rules, providing insight into underlying neural mechanisms. However, in many complex behaviors, syntax rules change over time, such as during learning or in response to new environmental and social contexts. Here, we investigated the songs of canaries, a seasonal songbird. Canaries learn a repertoire of 30-50 syllable types, produce syllables in repeat phrases, and organize these phrases into sequences with long-range syntactic dependencies (Markowitz 2013). Since canaries are known to adapt their repertoire annually (Nottebohm 1986), we recorded their songs during the spring mating season. We used our recently developed deep learning tools to annotate over 25,000 songs. This dataset allowed to track changes in the syntactic properties that determine syllable sequencing. Over days and weeks, we observed changes in syllable usage rates, syllable numbers within phrases, phrase positions in songs, and in the long-range dependencies of phrase transitions. Acoustic features of syllables were also found to shift alongside these syntactic changes. Quantifying the variability of these properties revealed that the observed changes were not random or uncorrelated. Most birds exhibited a global trend of moving between order and disorder in their song's syntactic and acoustic features. Interestingly, this trend differed between individuals; some birds increased their stereotypy and decreased variability across days, while others adopted more disordered and variable song structures. These findings demonstrate, for the first time, that canary syntax rules are dynamic in much shorter time scales than previously shown and establish canaries as a valuable animal model for studying the neural mechanisms underlying syntax rules plasticity in social and environmental adaptation, and in implementing individual-specific strategies.