Quantifying group size in the red fox: impacts of definition, season and intrusion by non‐residents

Abstract

AbstractDetermining group membership is fundamental to studies of social behaviour and monitoring population changes. However, this can be challenging for ecologically important solitary‐foraging carnivores such as red foxes, which have flexible social systems. We used camera‐traps to quantify seasonal changes in rates of territory intrusion by non‐residents and compared group definitions based on shared space use (spatial overlap) and social encounters (spatiotemporal overlap). Group sizes based on spatial overlap were overestimated but incorporating a minimum number of sightings (sighting threshold) improved accuracy. Groups defined by spatiotemporal overlap were similar in size to those based on spatial overlap with a sighting threshold but included different individuals, highlighting the challenges of determining group membership. Groups were smallest in spring and summer and largest in autumn and winter because all definitions failed to exclude non‐residents during the mating and dispersal seasons. However, non‐residents were recorded year‐round: over half were known or probable neighbours, and so may be relatives of territory residents. Strangers were most common in winter, when non‐residents were more likely to be males in search of extra‐group copulations. We conclude that groups of territorial, solitary foragers may be defined more accurately by combining patterns of space use, sighting frequency and social connectivity rather than considering these measures in isolation. When social information is not available, spatial overlap measures should include a sighting threshold. Surveying several adjacent territories concurrently helps identify the origins, and motivations, of non‐resident visitors.