Optimal time of the day to record bird songs for detecting changes of their breeding periods

概要

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We made a preliminary study on analyzing the changing levels of bird songs of the day in order to determine the peak level time zone efficiently from massive sound recording data. The data were collected at nine sites of forests from Hokkaido to Kochi Prefecture, southwestern Japan. The bird songs were recorded for 80 minutes, e.g. from 20 min. before, to 60 min. after sunrise using IC recorders. Our analyses showed that the peak song period of the day was ten minutes, e.g. from four min. before, to six min. after sunrise. However, three species, such as Treron sieboldii, Eophona personata and Phylloscopus coronatus, sang frequently in the later period. In addition, long-distance migratory birds tended to start singing later in the day on their first arrival day. Therefore, we recommend monitoring forest bird songs twice a day, namely once around sunrise and later e.g. approximately 60 minutes after sunrise.