Social influences on dispersal and the fat-tailed dispersal distribution in red-cockaded woodpeckers

Abstract

"Fat-tailed" distributions of dispersal distances involve long movements that do not appear to follow the normal distribution characterizing most short dispersals. Theorists have offered 2 nonexclusive explanations for such distributions. They suggest that the fat tail is a product of a single perturbed dispersal function, or that there may be multiple movement modes that widen dispersal distributions, or kernels, when considered simultaneously. We evaluated dispersal distances in the cooperatively breeding red-cockaded woodpecker (Picoides borealis) using a 22-year data set. Results illustrated that dispersal distances differed between juvenile and helper dispersers but not between sexes. Results further showed fat-tailed dispersal distributions in all social and sex classes. Then within juvenile females, we used radiotelemetry to document 2 fundamentally different dispersal strategies: Woodpeckers forayed from a natal area until breeding vacancies were located, and they made jumps to distant locations where birds continued to search for settlement options. Jumping was a behavior that added long-distance movements to the dispersal kernel and fattened the tail of the distribution. Our results are congruent with growing evidence that dispersal of animals typically does not represent a single process and that dispersers may switch between movement modes based on a complex relationship of internal state, landscape characteristics, motion capacity, and navigational ability. Rare and cryptic movement modes such as jumping may also account for the fat tail in the dispersal distance distributions of other species. © The Author 2010. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved.