Do predators modify context-dependent dispersal of red squirrels?

Abstract

Natal dispersal, the one-way movement between birth site and first breeding site, is an important determinant of species gene-flow and invasion potential. While dispersing in unfamiliar habitat, individuals may adjust their movement based on possible costs and benefits of moving, termed context-dependent dispersal. The role of factors, such as population density or spatial organisation of habitats, is well studied in the departure, transfer and settlement phases of dispersal. However, the role of predators for context-dependent dispersal remains less studied, particularly for the transfer phase and settlement phase of natal dispersal. We studied natal dispersal of radio-collared Eurasian red squirrels, Sciurus vulgaris, in relation to nest site locations of their main predator, the goshawk, Accipiter gentilis, in Finland. The locations of nest sites of goshawk had no influence on movement made during the transfer phase or on the location of settlement sites of juvenile red squirrels. Limited data on squirrel response to indices of predator presence (call playback of goshawk and faecal odours of mammalian predators) appeared to support the conclusion that predators had limited role in explaining movements of dispersers. We suggest that predators do not modify context-dependent dispersal among red squirrels in our boreal study area. This finding may be due to the low density of squirrel predators in northern boreal forests but may not hold true for species in which dispersers frequently encounter predators. Our study supports the conclusion that the resource and habitat availability are more important factors than predator presence for context-dependent dispersal among red squirrels. Context-dependent dispersal means that individuals rely on a set of external cues, such as local population density and habitat quality, to adjust their movement tactics. One potentially important but little studied factor for context-dependent dispersal is the presence of predators. We studied movements of radio-collared dispersing Eurasian red squirrels in relation to nest site locations of their main predator, the goshawk. Movements of dispersing red squirrels were not influenced by the presence of predators. Thus, it seems likely that food and habitat availability, which were previously observed to shape dispersal patterns of red squirrels, determine where and how far Eurasian red squirrels disperse in boreal forests.