When the Lévy breaks

Wagner T. Cassimiro “Aranha” / Flickr Creative Commons

The paper:

A.E. Edwards et al., “Revisiting Lévy flight search patterns of wandering albatrosses, bumblebees and deer,” Nature , 449:1044–48, 2007. (Cited in 53 papers)

The finding:

Andrew Edwards, with Fisheries and Oceans Canada, found that earlier reports had mistakenly attributed an optimal search pattern—called a Lévy flight, in which clusters of short journeys are interspersed with rare long-distance jumps—to the foraging behavior of wandering albatrosses, bumblebees, and deer. “The data were wrong,” says Edwards, who instead suggested that the animals come across food at simple random intervals.

The problems:

Data loggers fixed to albatrosses in 1992 incorrectly recorded nest-sitting as food searching time. The bumblebee and deer data were kosher, but researchers used “faulty methods” based on graphical approaches to infer Lévy flights for all three animals, Edwards says.

The alternative:

Edwards proposed a likelihood-based method that tests for power-law distributions—the hallmark of a Lévy flight—to more accurately verify the optimal search pattern. He is currently reanalyzing data from several other species of the so-called “Lévy fleet” (see below).

The holdouts:

Rothamsted Research’s Andy Reynolds used Edwards’s likelihood approach to show that honeybees use Lévy flights when relocating food sources ( Behav Ecol Sociobiol , in press). David Sims of the United Kingdom’s Marine Biological Association also demonstrated that several marine predators exhibit Lévy patterns ( Nature , 451:1098–1102, 2008). “The idea that animals follow Lévy flights is [still] a sound one,” says Reynolds.