Fig. 2: Horizontal position changes are accompanied by head turns.
a, Head and body orientation of bird Orange (ventral view) during one example of position changes to the right, tracked (sample rate: 120 Hz) in the footage of Camera 2. Circles: beak tip positions; plus signs: neck positions; upward pointing triangles: tail base positions. Cutouts of freeze frames of the footage taken with Camera 2 show the bird’s head and body posture for 11 time points during the position change. b, In all birds, the median angle of head turn during horizontal position change in flocking flight is positively correlated (linear mixed effects model (LMM), estimates ± s.e.m.: 2.05 ± 0.1, P < 0.001, t = 21.0) with the direction of position change relative to zero degrees in wind direction. Coloured dots: individual data points; coloured lines: fitted linear regression models (R2 values are indicated for each bird); colours: bird IDs. Negative values: left-hand positions in the flight section. n = 10 horizontal position changes per bird. c,d, Schematic representation of a bird head’s orientation (dorsal view) during straight flight (c) and during a horizontal position change to the right (d). The overall visual field of a zebra finch22 and spatial areas with high visual acuity23 are indicated in blue and yellow, respectively. Black arrow: direction of position change; grey arrow: wind direction. e, Head turn angles (red circles) and horizontal positions (blue circles) of bird Orange during the horizontal position change shown in a. Light red area: time period of significant head turn; light blue area: time period of significant position change; purple area: product of the overlap of the light red and blue areas; black line: time period shown in a; black dots: most lateral positions.
