Comparison of Visually Guided Flight in Insects and Birds

Abstract

Over the last half century, work with flies, bees, and moths have revealed a number of visual guidance strategies for controlling different aspects of flight. Some algorithms, such as the use of pattern velocity in forward flight, are employed by all insects studied so far, and are used to control multiple flight tasks such as regulation of speed, measurement of distance, and positioning through narrow passages. Although much attention has been devoted to long-range navigation and homing in birds, until recently, very little was known about how birds control flight in a moment-to-moment fashion. A bird that flies rapidly through dense foliage to land on a branch-as birds often do-engages in a veritable three-dimensional slalom, in which it has to continually dodge branches and leaves, and find, and possibly even plan a collision-free path to the goal in real time. Each mode of flight from take-off to goal could potentially involve a different visual guidance algorithm. Here, we briefly review strategies for visual guidance of flight in insects, synthesize recent work from short-range visual guidance in birds, and offer a general comparison between the two groups of organisms.

Keywords: flight speed; image expansion; optic flow; sensorimotor transformation; visuomotor control.

Figure 1

The flight of a bird through its natural environment requires that it make visually complex transitions, most of which have yet to be studied. The visual algorithms may include maintaining balanced optic flow or avoiding high optic flow, or maintaining constant velocity, acceleration, deceleration, height, rate of image expansion, or rate of change of time to collision.

Figure 2

Regulation of flight speed of Budgerigars in a tunnel displaying moving gratings on the walls. The red bars denote the change in flight speed induced by the moving gratings in comparison with stationary gratings, where positive pattern velocities represent grating motion in the birds' flight direction and negative pattern velocities represent grating motion in the opposite direction. The blue bars represent the changes in flight speeds that would be expected if the Budgerigars matched the changes of their flight speed to the speeds of grating motion, i.e., if they held the rate of image motion constant in their eyes. Adapted with permission from Schiffner and Srinivasan (2015).

Figure 3

Profiles of flight speed of Budgerigars in a tapered tunnel, of height 2.4 m, during flight in the narrowing direction (red) and in the widening direction (green). Adapted with permission from Schiffner and Srinivasan (2016), which provides further information and statistical analyses of the results.

Figure 4

Hummingbirds appear to use expansion cues for lateral course control. Black and red gratings depict the stationary visual patterns displayed on the left and right walls of the tunnel. Dashed lines are the average lateral positions, and shaded regions are the average extremes for birds at the halfway point through the tunnel. Black lines indicate the rate of vertical expansion for a bird moving laterally at 0.1 m/s, which is the typical maximum lateral flight speed. Adapted with permission from Dakin et al. (2016).

Figure 5

(A) Video-based visualization of Budgerigar flight through an aperture that is wider than the wingspan (left) and narrower than the wingspan (right). Image courtesy H. Vo and I. Schiffner. (B,C) Analysis of trajectories of Budgerigars approaching apertures of various widths, comparing flights through apertures that require wing closure (dashed curves) with flights through apertures that do not require wing closure (solid curves). Left: Mean profiles of flight speed; Right: Mean profiles of height. Adapted from Vo et al. (2016).