title: The use of network analysis to study complex animal communication systems: a study on nightingale song.
abstract: The singing of song birds can form complex signal systems comprised of numerous subunits sung with distinct combinatorial properties that have been described as syntax-like. This complexity has inspired inquiries into similarities of bird song to human language; but the quantitative analysis and description of song sequences is a challenging task. In this study, we analysed song sequences of common nightingales (Luscinia megarhynchos) by means of a network analysis. We translated long nocturnal song sequences into networks of song types with song transitions as connectors. As network measures, we calculated shortest path length and transitivity and identified the 'small-world' character of nightingale song networks. Besides comparing network measures with conventional measures of song complexity, we also found a correlation between network measures and age of birds. Furthermore, we determined the numbers of in-coming and out-going edges of each song type, characterizing transition patterns. These transition patterns were shared across males for certain song types. Playbacks with different transition patterns provided first evidence that these patterns are responded to differently and thus play a role in singing interactions. We discuss potential functions of the network properties of song sequences in the framework of vocal leadership. Network approaches provide biologically meaningful parameters to describe the song structure of species with extremely large repertoires and complex rules of song retrieval.
authors.affiliation: Institute of Biology, Animal Behaviour Group, Free University Berlin, , Berlin, Germany, Department of Exposition, Unit Epidemiology, Statistics and Mathematical Modelling, Federal Institute for Risk Assessment (BfR), , Berlin, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Weiss
authors.forename: Henrike
authors.initials: H
authors.lastname: Hultsch
authors.forename: Iris
authors.initials: I
authors.lastname: Adam
authors.forename: Constance
authors.initials: C
authors.lastname: Scharff
authors.forename: Silke
authors.initials: S
authors.lastname: Kipper
mesh_terms: D000818:Animals; D001604:Berlin; D008297:Male; D016571:Neural Networks, Computer; D020308:Songbirds / Q000502:physiology*; D014828:Vocalization, Animal
keywords: Luscinia megarhynchos; bird song sequence; network analysis; nightingale; syntax