Scale-free intermittent movements characterize animal searches: Analyses of high resolution search paths of four insect species

With the advent of the harmonic radar it has become possible to monitor the searching flight patterns of honeybees, bumblebees and butterflies over landscape scales (up to about 500 m). High-speed video has made it possible to record the searching flight patterns of drosophila in laboratory-scale experiments (up to about 1 m). Analysis reveals that the searching flights of these invertebrates are scale-free, and that they can be represented by a series of straight-line segments with lengths distributed according to an inverse-square law. This result, combined with the ‘no preferred direction' characteristic of the flights, demonstrate that these creatures adopt the same optimal search pattern. Frequently occurring short, slow flight paths are found to randomly alternate with rarer, longer, faster flight paths. This suggests that searching is intermittent, with active searching phases randomly alternating with fast, relocation phases. Scale-free searching patterns have been found microzooplankton, albatrosses, deer, spider monkeys and jackals. Many foragers (e.g. planktivorous fish and ground foraging birds) are known to adopt intermittent searching strategies. The results reported on here are the first reported examples of scale-free, intermittent searching. The durations of the searching and relocation phases are shown to obey a universal scaling relationship.