Abstract
Tracks of moving animals have many short moves interspersed with longer moves, and frequencies of all moves together often indicate Levy flights (a type of power law)1. The Levy flight foraging hypothesis suggests that, ‘since Levy flights and walks can optimize search efficiencies, therefore natural selection should have led to adaptations for Levy flight foraging1 and it has been apparently supported by several studies of large numbers of tracks of marine animals234. We show that Levy flights are caused by marine animals attempting to move in simple ways and they are unlikely to be evolved behavior. We do this by analyzing the tracks of autonomous underwater gliders which conform to Levy flights while they were programmed to perform simple directed movement. Gliders are autonomous underwater vehicles (AUV), propelled by a buoyancy engine5.The principle of operation is that by alternating positive and negative buoyancy, the winged AUV glides through the ocean in an undulating path, resurfacing after a pre-programmed number of undulations. During the periods at the surface, which typically last 15 minutes, GPS is used for positioning before and after transmission of data via a satellite link, whereas underwater the trajectory is deadreckoned from measured heading, pitch and pressure rate. Thus they are potentially a good analogy to a navigating animal which may also attempt to make directed movements using the best available (and often intermittent6) navigational information.
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