Figure 6. Field research on frog choruses, by using our sound-imaging method¹⁴.

(A) A photograph of a male Japanese tree frog (Hyla japonica). (B) A photograph of our sound-imaging device Firefly. The Firefly unit consists of a microphone and a light emitting diode (LED) that is illuminated when capturing nearby sounds¹⁴. (C) A photograph of a paddy field in Japan. Along one edge of this paddy field, we deployed 85 or 86 sound-imaging devices at intervals of 40 cm. As shown here, an index was attached to each device from one end of the edge, which was closer to the camera, to the other end. The spatio-temporal light pattern of these devices was recorded by a video camera. Note that the lights of some devices were not detected, when those devices were deployed far from the camera and were not illuminated by frog calls. We carefully checked all the data, and confirmed that the lights of at least 40 devices close to the camera were stably captured even when those were not strongly illuminated by frog calls. Hence, we used the light patterns of 40 devices close to the camera for data analysis of all the observations. These photographs were taken by I.A. and H.G.O.