Through the eyes of a bird: modelling visually guided obstacle flight

Abstract

Various flight navigation strategies for birds have been identified 9 at the large spatial scales of migratory and homing behaviors. However, relatively little is known about close range obstacle negotiation through cluttered environments. To examine obstacle flight guidance, we tracked pigeons (C. livea) flying through an artificial forest of vertical poles. Interestingly, pigeons adjusted their flight path only ~1.5m from the forest entry, suggesting a reactive mode of path planning. Combining flight trajectories with obstacle pole positions, we reconstructed the visual experience of the pigeons throughout obstacle flights. Assuming proportional-derivative (PD) control with a constant delay, we searched the relevant parameter space of steering gains and visuomotor delays that best explained the observed steering. We found that a pigeon’s steering resembles proportional control driven by the error angle between the flight direction and the desired opening, or gap, between obstacles. Using this pigeon steering controller, we simulated obstacle flights and showed that pigeons do not simply steer to the nearest opening in the direction of flight or destination. Pigeons bias their flight direction toward larger visual gaps when making fast steering decisions. The proposed behavioral modeling method converts the obstacle avoidance behavior into a (piece-wise) target-aiming behavior, which is better defined and understood. This study demonstrates how such an approach decomposes open-loop free-flight behaviors into components that can be independently evaluated.