A Comparative Study Of Bird Song Complexity Measures
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|Tila||Julkaistu - 2012|
It is known that the song repertoire and versatility of the male Pied Flycatcher (Ficedula hypoleuca) correlate significantly with the amount of previous experience (older males have larger repertoire size), with the brightness of colour (differences between brown and black males), body mass and physical condition and the spring arrival order. Thus the species is an interesting test case for song complexity measures. Espmark and Lampe (Bioacoustics, 1993, Vol. 5, pp. 33 – 65) analysed the song complexity of male Pied Flycatcher with several different measures including number of elements and number of element types in the phrase and repertoire size. The song element is defined as the smallest (visually) separable entity in the spectrogram. Elements in turn are building blocks of syllables. A string of syllables that occur together in a particular pattern is called a phrase. In our study only phrase level complexity is considered. Da Silva and Vielliard (Advances in Bioacoustics 2, pp. 185-204) claim that repertoire size is inadequate for measuring the degree of monotonity or diversity of the song and propose the use of entropy or self-information as a complexity measure. We apply both of these approaches in this paper and compare how well the measures predict the age and physical condition of the singing male. The test data consists of male Pied Flycatcher songs recorded in Ruissalo Island, Turku, Finland, by Päivi Sirkiä with her students in 2006 – 2008.