Supplementary Figure 9: Vocalization spectra measured with backpack microphones and accelerometers
From: Reconstruction of vocal interactions in a group of small songbirds
(a-d) show median vocalization spectra (solid lines) of birds 1-4 recorded with microphones #1 to #4. Spectra were computed from 166-ms fragments starting with vocalization onsets (calls, introductory notes and syllables). Only vocalizations that did not overlapped with vocalizations or noises (e.g. wing flaps) produced by other animals were selected. In birds 1-4 the numbers of such vocalizations were 972, 4535, 3344, and 1468, respectively. Dotted lines represent background noise recorded by microphones when no bird vocalized. To compute spectra of background noise, 10000 166-ms sound fragments during quiescence were randomly taken. Note that sound intensity at the microphone of the vocalizing bird exceeded background noise by about 30 dB. Sound intensity at microphones of listeners exceeded background noise by about 20 dB. Spectra at the microphones of listeners were attenuated but similar to spectra at carrier microphones. SPL values are given relatively to 10-6 Pa/
. (e-h) show median vocalization spectra (solid lines) of birds 1-4 recorded with accelerometers #1 to #4. Dotted lines represent spectra of background noise when no bird vocalized. The peak in the vicinity of 8 kHz is caused most probably by resonance of the accelerometer sensor (luckily, the resonance frequency lies above the frequency range of interest). Note that the spectra of the listeners essentially does not differ from their background noise spectrum. The spectra of the vocalizing birds exceed the background noise spectra by about 20 dB at 1 kHz. Acceleration values are provided relative to 10-5 m/s2/.
