How lovebirds maneuver through lateral gusts with minimal visual information

Abstract

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.

Sensory gaze stabilization in echolocating bats

“…Monkeys, for example, performed pitch and yaw head rotations while scanning the environment, but kept a steady gaze when they focused on a target [28]. In landing experiments, it has been shown that, similar to our bats, lovebirds kept a steady gaze in all axes ( pitch, yaw and roll) relative to a target, but more often in the second half of the flight, where there was a need for high precision during landing [14]. Zebra finches used head saccades in order to adjust their horizontal gaze while avoiding an obstacle and going through a window [13].…”

“…Several previous studies found that animals stabilize their gaze during different tasks such as walking [2,6,9,15], running [28], flying [9][10][11]13], landing [14] and hovering [8,12], but more relevant to our study, relative to a target, where it has been shown that the fixation occurred after identifying a target. Monkeys, for example, performed pitch and yaw head rotations while scanning the environment, but kept a steady gaze when they focused on a target [28].…”

“…This response, known as the vestibulo-collic reflex, has also been observed in other primates [5,6], where it has been hypothesized to be activated only when there is a need to lock the gaze, for example, on a target. In birds, several studies suggested a gaze stabilization mechanism [7][8][9][10][11][12][13][14]. For example, the head bobbing behaviour of pigeons has been extensively studied, and it probably functions to stabilize visual gaze [15].…”

How to extract energy from turbulence in flight by fast tracking

“…Quinn et al. (2019) show that birds responded effectively to unsteady flows given even limited sensory information. Katzmayr (1922) shows that fixed-wing aircraft can extract the energy in random gusts by clever transient rotations of the net aerodynamic force vector.…”

Optimization of avian perching manoeuvres

“… Perching at speed is amongst the most challenging flight behaviours that birds perform 1,2 , and beyond the capability of current autonomous vehicles. Smaller birds may touchdown by hovering 3-8 , but larger birds typically swoop upward to perch 1,2 – presumably because the adverse scaling of their power margin prohibits slow flapping flight 9 , and because swooping transfers excess kinetic to potential energy 1,2,10 . Perching is risky in larger birds 6,11 , demanding precise control of velocity and pose 12-15 , but it is unknown how they optimize this challenging manoeuvre.…”