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 distributioncharacterizing most short dispersals. Theorists have offered 2 nonexclusive explanations for such distributions. They suggest thatthe fat tail is a product of a single perturbed dispersal function, or that there may be multiple movement modes that widen dis-persal distributions, or kernels, when considered simultaneously. We evaluated dispersal distances in the cooperatively breedingred-cockaded woodpecker (Picoides borealis) using a 22-year data set. Results illustrated that dispersal distances differed betweenjuvenile and helper dispersers but not between sexes. Results further showed fat-tailed dispersal distributions in all social and sexclasses. Then within juvenile females, we used radiotelemetry to document 2 fundamentally different dispersal strategies: Wood-peckers forayed from a natal area until breeding vacancies were located, and they made jumps to distant locations where birdscontinued to search for settlement options. Jumping was a behavior that added long-distance movements to the dispersal kerneland fattened the tail of the distribution. Our results are congruent with growing evidence that dispersal of animals typically doesnot represent a single process and that dispersers may switch between movement modes based on a complex relationship ofinternal state, landscape characteristics, motion capacity, and navigational ability. Rare and cryptic movement modes such asjumping may also account for the fat tail in the dispersal distance distributions of other species. Key words: dispersal, fat taildistribution, kurtosis, movement ecology, Picoides borealis, red-cockaded woodpecker. [Behav Ecol]