Revisiting Lévy flight search patterns of wandering albatrosses, bumblebees and deer

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Abstract
Levy flights are random walks characterised by many short steps and rare long steps. They display fractal properties, have no typical scale, and occur in physical and chemical systems. On the basis of high-resolution data and new analyses, previous claims that wandering albatrosses perform Levy flights when searching for prey on the ocean surface are shown to be unfounded. A new method is proposed for use when testing for power-law distributions. The study of animal foraging behaviour is of practical ecological importance1, and exemplifies the wider scientific problem of optimizing search strategies2. Lévy flights are random walks, the step lengths of which come from probability distributions with heavy power-law tails3,4, such that clusters of short steps are connected by rare long steps. Lévy flights display fractal properties, have no typical scale, and occur in physical3,4,5 and chemical6 systems. An attempt to demonstrate their existence in a natural biological system presented evidence that wandering albatrosses perform Lévy flights when searching for prey on the ocean surface7. This well known finding2,4,8,9 was followed by similar inferences about the search strategies of deer10 and bumblebees10. These pioneering studies have triggered much theoretical work in physics (for example, refs 11, 12), as well as empirical ecological analyses regarding reindeer13, microzooplankton14, grey seals15, spider monkeys16 and fishing boats17. Here we analyse a new, high-resolution data set of wandering albatross flights, and find no evidence for Lévy flight behaviour. Instead we find that flight times are gamma distributed, with an exponential decay for the longest flights. We re-analyse the original albatross data7 using additional information, and conclude that the extremely long flights, essential for demonstrating Lévy flight behaviour, were spurious. Furthermore, we propose a widely applicable method to test for power-law distributions using likelihood18 and Akaike weights19,20. We apply this to the four original deer and bumblebee data sets10, finding that none exhibits evidence of Lévy flights, and that the original graphical approach10 is insufficient. Such a graphical approach has been adopted to conclude Lévy flight movement for other organisms13,14,15,16,17, and to propose Lévy flight analysis as a potential real-time ecosystem monitoring tool17. Our results question the strength of the empirical evidence for biological Lévy flights.