Fig. 2

Diurnal pattern of measurement parameters in a free-swimming Risso’s dolphin. Temperature of the muscle–blubber interface (Tmbi, A) and external acceleration averaged over 60 s (EA₆₀, B) were plotted every 15 min. EA₆₀ data are shown in the figure as log-transformed data to make it easier to visualize the variation. Heart rate (HR, C) was plotted hourly. The black lines indicate the mean across the 11 days at each time point, and the gray ribbons indicate the standard deviation. The gray points show the individual data. The bars on the top indicate the bay swimming time (gray: 10:00–16:00), and those on the bottom indicate the night phase (black: 0:00–6:00 and 17:15–24:00), which approximately correspond to three characteristic periods of “during the daytime”, “before sunrise”, and “after sunset”