Things That Sing In The Night: Melodic And Rhythmic Intervals In A Nocturnal Bird

Do birds sing notes with specific melodic and rhythmic intervals? The use of small intervals of less than 750 cents and rhythmic categories such as isochrony are some of the cross-cultural statistical universals that characterise human musical production. However, a growing body of research has shown that different species of songbirds also use similar musical properties in their songs. Notably, these studies have focused only on diurnal species, leaving out nocturnal birds, which also have extensive vocal repertoires. To address this knowledge gap and demonstrate that these musical characteristics extend beyond songbirds, in this study we decided to test whether similar universal statistics were also present in nocturnal species, exemplified by the Eurasian Scops Owl (Otus scops). We analysed the notes that constitute the songs of this species focusing on prominent acoustic features identified by previous literature, i.e. the minimum-to-maximum frequency ratio and inter-onset intervals. Our findings unveil that the songs of the Eurasian Scops Owl are distinguished by melodic and rhythmic intervals—specifically Huygens' tritone and isochrony—rather than arbitrary values. Our results show that such musical properties are widespread in the avian class and, as they are not unique to humans, can be considered a promising statistical universal in animal vocal communication.