Figure 3.

Flight behaviour in an oscillating drum. The outer drum sinusoidally oscillated back and forth at a frequency of 3.1 Hz with 38° peak-to-peak amplitude. (a) The roll angle of the bee's head (solid black line) follows pattern movement (dashed black line). Bees still make fast thorax roll oscillations (solid grey line), similar to those seen in the experiments with the stationary drum (figure 2). (b) Probability density of head orientation relative to the horizontal (3400 data points). Head and drum orientation vary over approximately the same range (black and black dashed line, respectively), indicating that head orientation is stabilized with respect to the visual environment (compare with figure 2a). (c) Difference between head and drum orientation (black) and between thorax and drum orientation (grey). The probability density function of head orientation relative to the oscillating drum (black) has a narrow peak around 0°, which is similar to the peak obtained for the stationary condition (dashed grey lines, taken from figure 2a). (d) The power spectra for head (black) and drum orientation (dashed black line) both have a peak at the same frequency (3.1 Hz), indicating that this stabilization reflex is based on visual information. While the head is clamped to the rotating drum, the thorax orientation power spectrum (grey line) has two distinct peaks. In addition to the peak around 6 Hz, which is the same frequency as for the spontaneous thorax roll oscillations in a stationary drum (figure 2b), there is also a peak at 3.1 Hz (stimulus frequency). Inset: head stabilization is very fast; the cross-covariation between head movement and pattern movement shows no pronounced time lag.