How lovebirds maneuver through lateral gusts with minimal visual information

Abstract

Significance Pilots need complex instruments and training to safely fly through gusts when their vision is deprived. In contrast, birds fly reliably over open water and at night, despite being more susceptible to gusts due to their much lower flight speeds. We found that even inexperienced lovebirds can navigate through strong opposing gusts in the dark, with only a faint point light source as a beacon. Their ability is surprising, because it was previously thought that diurnal animals needed a visual horizon and image features moving over their retina to maneuver. Instead, lovebirds fixate their head on the beacon while reorienting their body into the gust like a weathervane, enabling them to infer gust angle via neck twist and compensate accordingly. Flying birds maneuver effectively through lateral gusts, even when gust speeds are as high as flight speeds. What information birds use to sense gusts and how they compensate is largely unknown. We found that lovebirds can maneuver through 45° lateral gusts similarly well in forest-, lake-, and cave-like visual environments. Despite being diurnal and raised in captivity, the birds fly to their goal perch with only a dim point light source as a beacon, showing that they do not need optic flow or a visual horizon to maneuver. To accomplish this feat, lovebirds primarily yaw their bodies into the gust while fixating their head on the goal using neck angles of up to 30°. Our corroborated model for proportional yaw reorientation and speed control shows how lovebirds can compensate for lateral gusts informed by muscle proprioceptive cues from neck twist. The neck muscles not only stabilize the lovebirds’ visual and inertial head orientations by compensating low-frequency body maneuvers, but also attenuate faster 3D wingbeat-induced perturbations. This head stabilization enables the vestibular system to sense the direction of gravity. Apparently, the visual horizon can be replaced by a gravitational horizon to inform the observed horizontal gust compensation maneuvers in the dark. Our scaling analysis shows how this minimal sensorimotor solution scales favorably for bigger birds, offering local wind angle feedback within a wingbeat. The way lovebirds glean wind orientation may thus inform minimal control algorithms that enable aerial robots to maneuver in similar windy and dark environments.