A stochastic movement model reproduces patterns of site fidelity and long-distance dispersal in a population of Fowler's toads ( Anaxyrus fowleri )

Although amphibians typically exhibit high site fidelity and low dispersal, they do undertake rare, long-distance movements. The factors influencing these events remain poorly understood, partly because amphibian spring movements tend to radiate from breeding sites and the animals are often difficult to locate at other times of the year. In this study, we investigate whether these movement patterns can be reproduced by a parsimonious model where foraging steps follow a heavy-tailed, Lévy alpha-stable distribution and individuals may either return to a previous refuge site or establish a new one. We consider three versions of the return behaviour: (1) a distance-independent probability of return to any previous refuge; (2) constant probability of return to the nearest refuge; or (3) a distance-dependent probability of return to each refuge. Using approximate Bayesian computation, we fit each version of the model to radiotracking data from a population of Fowler's Toads, which inhabits a linear sand dune habitat on the north shore of Lake Erie in Ontario, Canada. Only the model with distance-independent, random returns provides a good fit of the inter-refuge distance distribution and the number of refuges visited per toad. Our results suggest that while toads occasionally forage over long distances, the establishment of new refuges is not driven by the minimization of energy expenditure.