. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Vd = + r= 10 20 Height, cm 30 250 "-150 •100 50 10 0. 5 " •' = + O r = 20 Height, cm 30 40 Figure 2. (a, h) Variation of horizontal flight speed (V,) with height (/;) above the surface, for two landing trajectories, (c. d) Variation of descent speed (V;) with height (/;) above the surface, for two landing trajectories. The straight lines are linear regressions through the data, as represented by the equations; r denotes the regression coefficient. Adapted from Srinivasan et al. (2000).
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Vd = + r= 10 20 Height, cm 30 250 "-150 •100 50 10 0. 5 " •' = + O r = 20 Height, cm 30 40 Figure 2. (a, h) Variation of horizontal flight speed (V,) with height (/;) above the surface, for two landing trajectories, (c. d) Variation of descent speed (V;) with height (/;) above the surface, for two landing trajectories. The straight lines are linear regressions through the data, as represented by the equations; r denotes the regression coefficient. Adapted from Srinivasan et al. (2000). surface at a relatively shallow descent angle. Second, land- ing bees tend to hold the angular velocity of the image of the ground constant as they approach it. What is the significance of holding the angular velocity of the image of the ground constant during landing? One important consequence is that the horizontal speed of flight is automatically reduced as the height decreases. In fact, by holding the image velocity constant, the horizontal speed is regulated to be proportional to the height above the ground, so that when the bee finally touches down (at zero height), her horizontal speed is zero, thus ensuring a smooth landing. The attractive feature of this simple strategy is that it does not require explicit measurement or knowledge of the speed of flight, or the height above the ground. Thus, stereoscopic methods of measuring the distance of the surface (which many insects probably do not possess) are not required. What is required, however, is that the insect be constantly in motion, because the image motion resulting from the in- sect's own motion is crucial in controlling the landing. The above strategy ensures that the bee's horizontal speed is zero at touchdown, but it does not regulate the descent speed. How is the descent speed controlled? Plots of descent speed versus height reveal a linear relationship between these two variables, as well. Two examples are
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
