A Typological Analysis of the Hoot of the Ryukyu Scops Owl Across Island Populations In the Ryukyu Archipelago and Two Oceanic Islands

The Ryukyu Scops Owl, Otus elegans, is distributed over a 1,200-km area, only inhabiting islands. Within this range, I studied this species across 20 continental islands in the Ryukyu Archipelago and two oceanic islands. Although most studies recently use quantitative continuous measurements of many specific aspects of the vocalization, I introduced a new method, “typological analysis” to visually classify variation of spectrograms according to the shape of syllable in the owl species, examining their dialects in relation to their geographical distribution. In the typological analysis, hoot, syllable, and element types were defined according to the number of syllables, the degree of timescale overlap of the first and second elements in the second syllable, and relative differences of duration and frequency of two elements in the second syllable, respectively. Although frequencies of hoot and element types in each island population were significantly different between the island groups north and south of the Kerama Gap across the archipelago, hoot and element types were shared between the island groups. Furthermore, typological variation occurred in syllable types, however there were no differences in frequencies of syllable types between the island groups. Geographic structure in vocal parameters as steep clines with stepped variation is represented as a dialect. According to the definition, this study found that no unique dialects in hoots occurred between the different island populations of Ryukyu Scops Owls. The Kerama Gap might act as a biogeographical barrier, contributing to the differentiation between owl hoots according to spectrotemporal analyses; however, the typological analysis detected the distribution of typological characteristics of hoots on the small islands north of the Kerama Gap that contradicts this concept of a biogeographical barrier. Because the typological analysis needs to visually examine each individual by careful attention to detail, it is a good method for discovering minor geographic variations and patterns in bird vocalizations.