English: Effect of changing the upper limit of cropped spectra on amplitude distribution. For the same colony (colony 6), overnight histograms of amplitude distribution are shown (top figure), when the upper limit of the cropped spectra (bottom figure) is increased from 255 to 800 Hz, whilst the lower limit is kept at 10 Hz. The effects are large and varied. To start with, most amplitude distributions exhibit two peaks, although some have one or three peaks. As the upper limit becomes larger than 400 Hz, a steady states emerges, gradually leading to extremely well defined unique maxima for each night under investigation. The oscillation of interest in our study is seen with the highest contrast for an upper limit around 600 Hz.