Abstract
Changes in flight direction in flying insects are largely due to roll, yaw and pitch rotations of their body. Head orientation is stabilized for most of the time by counter rotation. Here, we use high-speed video to analyse head- and body-movements of the bumblebee Bombus terrestris while approaching and departing from a food source located between three landmarks in an indoor flight-arena. The flight paths consist of almost straight flight segments that are interspersed with rapid turns. These short and fast yaw turns (“saccades”) are usually accompanied by even faster head yaw turns that change gaze direction. Since a large part of image rotation is thereby reduced to brief instants of time, this behavioural pattern facilitates depth perception from visual motion parallax during the intersaccadic intervals. The detailed analysis of the fine structure of the bees’ head turning movements shows that the time course of single head saccades is very stereotypical. We find a consistent relationship between the duration, peak velocity and amplitude of saccadic head movements, which in its main characteristics resembles the so-called "saccadic main sequence" in humans. The fact that bumblebee head saccades are highly stereotyped as in humans, may hint at a common principle, where fast and precise motor control is used to reliably reduce the time during which the retinal images moves.
Highlights
Salient objects can help insects like bees, wasps and ants to accurately find their way back home and to newly discovered food sources [1,2]
Recent experiments with landmarks that were camouflaged by carrying the same texture as the background, suggest that honeybees can exploit dynamic cues like the optic flow pattern to pinpoint the goal location [10]
Why is it so important to control gaze orientation? We assume that facilitation of depth perception from motion parallax is one important reason, because visual mechanisms that exploit the translational components of optic flow for odometry or depth perception are likely to break down, if contaminated by strong rotational optic flow
Summary
Salient objects can help insects like bees, wasps and ants to accurately find their way back home and to newly discovered food sources [1,2]. In experiments that are designed to find out what features of the environment the homing insects use, the experimenters often allow the animals to become accustomed to distinct visual features close to the place of interest, i.e. their feeding site, and displace or modify these landmark cues with the aim of observing where and how the animals search for the goal. From such experiments it is clear that insects can use the retinal size and position, the colour, distance and texture of landmarks, [3,4,5,6,7,8] as well as skyline elevations for homing [9]. Recent experiments with landmarks that were camouflaged by carrying the same texture as the background, suggest that honeybees can exploit dynamic cues like the optic flow pattern to pinpoint the goal location [10].
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