Canary Mating Season Songs Move 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 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. In this study, we investigated the songs of canaries, a seasonal songbird species. 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. Since canaries are known to adapt their repertoire annually, we recorded their songs during the spring mating season and examined 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. Most birds exhibited a clear trend of moving between order and disorder in their songs syntactic and acoustic features. Interestingly, this trend varied across individuals; some birds increased their stereotypy and decreased variability across days, while others adopted more disordered and variable song structures. These findings establish canaries as a valuable animal model for studying the neural mechanisms underlying syntax rules in complex motor sequences, their plasticity in social and environmental adaptation, and in implementing individual-specific strategies.