Fig. 2.

The neck isolates the head from body motion and orients it toward the goal based on minimal visual information. (A) The difference between head and body attitude determines neck pitch, roll, and yaw joint angles. Angles are defined by an arena-based inertial frame (x, y, z) that translates with the body. (B) The first flight by bird BB in the cave–cross environment shows how the neck isolates the head from body motion over multiple timescales. (C) For each bird (N = 3; separated by bird in SI Appendix, Figs. SF6–SF8), neck angle is correlated with body angle, which stabilizes the head in pitch, roll, and yaw over both low and high frequencies (LF, < 8.5 Hz; HF, > 8.5 Hz; Materials and Methods). Body–neck slopes are close to 1 at high frequencies (visual conditions pooled: pitch LF, 1.04, R² 0.90; pitch HF, 1.02 R² 0.76; roll LF, 0.87, R² 0.65; roll HF, 1.02, R² 0.90; yaw LF, 0.75, R² 0.76; yaw HF, 1.01, R² 0.81).