Figure 1.

Bats maintain a fixed vertical gaze (α) despite the jitter in body pitch. (a) Schematic showing the angles, which we refer to in this figure including α—the vertical gaze relative to target and β— the body-to-target vertical angle. (b) Vertical gaze (α), wing-movement and body-to-target angle (β) in two exemplary flights. Top trace—body-to-target angle (β red) demonstrates the body jitter during flight. The grey shadings represent half wingbeat cycle (estimated from the wings' elevation, see the electronic supplementary material, figure S11). Bottom—the vertical gaze (α light blue). The y-axis is divided into two parts (with a gap) to increase visibility, but the y-scale of both parts is identical. The arrows show the locking point. (c) The distribution of the vertical gaze (α) in darkness (light blue line) and in light (grey dashed line), and the body-to-target angles (β, red line). The mean and s.e. are presented for all bats (n = 8 for the head and body in dark, n = 3 for light). All distributions were centred around ‘0’ to allow comparison. The horizontal lines represent the width at half height for the different distributions. (d) The angle between the head and the body (γ, brown line, see schematic) was correlated to body pitch (δ, green line; see schematic). A single trial is presented. (e) Head–body angle (γ) versus body pitch (δ)—same as in (d) but for all bats and all trials (n = 6, two bats were excluded owing to insufficient tracking of γ).