How biomechanics, path planning and sensing enable gliding flight in a natural environment

Abstract

Gliding animals traverse cluttered aerial environments when performing ecologically relevant behaviours. However, it is unknown how gliders execute collision-free flight over varying distances to reach their intended target. We quantified complete glide trajectories amid obstacles in a naturally behaving population of gliding lizards inhabiting a rainforest reserve. In this cluttered habitat, the lizards used glide paths with fewer obstacles than alternatives of similar distance. Their takeoff direction oriented them away from obstacles in their path and they subsequently made mid-air turns with accelerations of up to 0.5 g to reorient towards the target tree. These manoeuvres agreed well with a vision-based steering model which maximized their bearing angle with the obstacle while minimizing it with the target tree. Nonetheless, negotiating obstacles reduced mid-glide shallowing rates, implying greater loss of altitude. Finally, the lizards initiated a pitch-up landing manoeuvre consistent with a visual trigger model, suggesting that the landing decision was based on the optical size and speed of the target. They subsequently followed a controlled-collision approach towards the target, ending with variable impact speeds. Overall, the visually guided path planning strategy that enabled collision-free gliding required continuous changes in the gliding kinematics such that the lizards never attained theoretically ideal steady-state glide dynamics.

Tails stabilize landing of gliding geckos crashing head-first into tree trunks

“…Unlike powered fliers, specialized gliders without flapping wings that include flying squirrels, colugos, lizards, snakes, and frogs steer toward landing targets at relatively high speeds and can experience large peak forces at landing while using their limbs, body, or extended skin surfaces 22 , 25 – 27 . Flying lizards from the genus Draco extend their ribs to attain high glide ratios and can orient their body to be nearly parallel with the surface just before touchdown with all legs simultaneously to slow down and facilitate attachment 11 , 26 , 28 . The flying Gecko, Ptychozoan kuhli , passively unfurls two large cutaneous flaps laterally between the front and rear legs along with interdigital webbing actively deployed by toe spreading 29 .…”

“…1 and Supplementary Movie 1 ). We expected that geckos would use a controlled-collision landing strategy as observed in wild, freely behaving flying lizards 11 (genus Draco , several species of which are sympatric with H. platyurus ). To our surprise, the geckos crashed head-first into tree trunks during subcritical (i.e., with insufficient distance to reach a steady, equilibrium glide), short-range glides 12 and appeared to stabilize landing using, once again, their remarkably versatile tails (Fig.…”

Combined effects of body posture and three-dimensional wing shape enable efficient gliding in flying lizards

“…The field site was an abandoned areca nut plantation located within the Agumbe Rainforest Research Station campus, Karnataka, India (13°31′04″ N, 75°05′18″ E) and previously described in Khandelwal and Hedrick, 2020 11 (Fig. S2 a).…”

“…Four data collection pauses of two days each were uniformly interspersed during the data collection period to reduce the effects of the team’s presence on lizard behavior at the field site. Glides were recorded between 9 am and 4 pm each day based on previous observations of lizard activity at the field site 11 . A complete glide recording began with capturing lizard(s) from the site and releasing them on the bottom of the takeoff tree in the motion capture arena.…”

“…1 a and movie S1 ). Together, these dynamic changes in the animal’s body posture and morphology, and consequently the aerodynamic force production, allows the animal to execute a variety of glide trajectories and achieve different tasks including mating, foraging, territoriality, and predatory avoidance, while accommodating their habitat’s spatial complexity 11 .

Figure 1 Illustration of the body posture and forces acting during a glide and the field motion capture arena.

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