LAUSR

ABSTRACT The sociality of the Arctic fox has been extensively studied during the breeding season, so that its summer territorial and generally monogamous social systems are now well described. A key knowledge gap remains, however, during the winter season, when logistic challenges preclude detailed observation of individuals. We have studied the socio-spatial winter dynamics of Arctic fox pairs to determine: (1) winter fidelity of Arctic fox pair mates to their summer home range; (2) the degree to which extraterritorial movements are simultaneous between pair mates; and (3) spatial proximity between pair mates when they perform simultaneous extraterritorial movements. To meet these objectives, 15 Arctic fox pairs from Bylot Island (Nunavut, Canada) were tracked during at least one winter in 2007–2011, using Argos satellite collars, for a total of 21 pair-years. Arctic foxes were generally faithful to their summer home ranges during winter, but some variation occurred among pairs. The degree of territory fidelity was highly correlated between pair mates. When foxes did extraterritorial movements, they performed excursions that were short in duration and generally not synchronized among pair mates. When pair mates were outside the territory at the same time, they did not travel together and rather foraged independently. We discuss some ecological implications of our findings, and suggest that different patterns may be observed in other Arctic fox populations. If such is the case, replicating our study in other parts of the species range will allow productive hypothesis testing regarding the determinants of Arctic fox winter sociality.