Rules to fly by: pigeons navigating horizontal obstacles limit steering by selecting gaps most aligned to their bearing

Citation:

Ros IG, Bhagavatula PS, Lin HT, Biewener AA. Rules to fly by: pigeons navigating horizontal obstacles limit steering by selecting gaps most aligned to their bearing. Roy. Soc. Interface Focus. 2017;7 (20160093).

Abstract:

Flying animals must successfully contend with obstacles in their natural
environments. Inspired by the robust manoeuvring abilities of flying animals,
unmanned aerial systems are being developed and tested to improve flight
control through cluttered environments. We previously examined steering
strategies that pigeons adopt to fly through an array of vertical obstacles
(VOs). Modelling VO flight guidance revealed that pigeons steer towards
larger visual gaps when making fast steering decisions. In the present experiments,
we recorded three-dimensional flight kinematics of pigeons as they
flew through randomized arrays of horizontal obstacles (HOs). We found
that pigeons still decelerated upon approach but flew faster through a
denser array of HOs compared with the VO array previously tested. Pigeons
exhibited limited steering and chose gaps between obstacles most aligned to
their immediate flight direction, in contrast to VO navigation that favoured
widest gap steering. In addition, pigeons navigated past the HOs with more
variable and decreased wing stroke span and adjusted their wing stroke
plane to reduce contact with the obstacles. Variability in wing extension,
stroke plane and wing stroke path was greater during HO flight. Pigeons
also exhibited pronounced head movements when negotiating HOs, which
potentially serve a visual function. These head-bobbing-like movements
were most pronounced in the horizontal (flight direction) and vertical directions,
consistent with engaging motion vision mechanisms for obstacle
detection. These results show that pigeons exhibit a keen kinesthetic sense of
their body and wings in relation to obstacles. Together with aerodynamic flapping
flight mechanics that favours vertical manoeuvring, pigeons are able to
navigate HOs using simple rules, with remarkable success.