The Hakubi Project

   In human speech, words often convey independent meanings and syntax allows combining multiple words into more complex, compositional expressions. In contrast, animal communication signals have typically been considered as motivational: vocalizations merely reflect emotion or arousal of signalers and do not provide compositional messages even when multiple units are combined. However, recent field studies have challenged this assumption by showing that several species of birds and nonhuman primates may be able not only to assign independent meanings to acoustically discrete vocalizations, but also to combine these signals into higher lexical sequences. In this talk, I introduce my recent studies on vocal communication in a small bird species, the Japanese tit (Parus minor). Japanese tits produce acoustically discrete calls in a variety of contexts, such as when encountering a predator and when facilitating group cohesion. Field experiments have revealed that these calls may not merely reflect arousal of signalers, but also convey information about external referents, such as the presence of a predator. In addition, these birds are able to combine meaningful calls into higher structured sequences according to an ordering rule. Playback experiments revealed that receiver tits are able to use an ordering rule to extract compound meanings from call sequences even if these sequences are composed of novel combinations of calls. These findings demonstrate previously unknown parallels between bird calls and human language, opening new avenues for exploring the origins and evolution of linguistic capabilities.