Dorning, J. and Harris, S. (2019), Quantifying group size in the red fox: impacts of definition, season and intrusion by non‐residents. Journal of Zoology, vol. 308, issue 1, pp. 37-46. https://doi.org/10.1111/jzo.12650
Despite being one of the most familiar British mammals, there are still huge gaps in our knowledge about red foxes, especially their social lives. Although we have long known that foxes live in mixed groups of adult males and females, how these groups operate remains a mystery. I cannot even guess at how many thousands of hours I spent on foot following radio-collared foxes around the streets of Bristol but, despite all this effort, fox sightings were infrequent. When I did see a fox, it was invariably alone. Even when two foxes met during their nightly perambulations, the encounters were normally cursory and involved little social interaction.
Watching foxes at night gives the impression that, because foxes forage alone, they do not have strong social bonds, and this led to terms such as primitively social, facultatively social, and living in spatial groups, being used to imply that foxes share a common area but are basically solitary. However, glimpses into the nocturnal lives of foxes are misleading: because they are mostly active at night, we tend to ignore what foxes do in the day.
It has long been known that wolves use den sites from mid-March to mid-June, when their cubs are young, and move them to rendezvous sites from mid-May to mid-October. These are typically areas of dense vegetation where they lie up for the day, and are a focus of social activity. What is not generally appreciated is that foxes do exactly the same, although they use rendezvous sites throughout the year, albeit less intensively in winter. As with wolves, fox rendezvous sites are secluded areas, typically with long grass and/or brambles. I am lucky in that I live in the middle of my long-term study area in Bristol, and the garden next door is overgrown – an ideal rendezvous site, and the perfect opportunity to get an insight into fox social life.
My rendezvous site is used intensively: foxes come and go through the day, with enthusiastic greetings of many arrivals (even though they may well have been ‘encountered’ the previous night), social grooming, play sessions, and the occasional show of dominance or a fight. Unfortunately, while rendezvous sites are the focus of fox social life, the dense vegetation makes it very hard to study their behaviour or recognise individual foxes.
However, while foxes forage alone, they visit many of the same food patches, albeit generally at different times of night. So to estimate group sizes, Jo Dorning and I placed camera traps at four or five of the best foraging patches (i.e. the gardens where the foxes were fed the most!) in each of seven territories in north-west Bristol for a year, and photographed all the foxes that came to be fed. It sounds easy, and in practice getting the photos was not too difficult: the challenge was identifying every fox in 124,808 photos! Fortunately, that job fell to Jo: she managed to identify 175 different foxes over five months old (we excluded cubs because they are even more difficult to identify than older foxes).
This was a staggering number of foxes and far more than we had anticipated. We expected that foxes from neighbouring groups, and even further afield, would visit occasionally, but it turned out that most of the foxes we photographed on each territory were not residents. When foxes disperse, they often move into an adjacent social group, and so it was no great surprise that they visited home: but we were amazed how often they did. From our earlier work we also knew that, in winter, there is a great deal of movement by males running between territories looking for mating opportunities and/or dispersing.
All this made it very hard to work out which foxes really were members of the social group and which were visitors. In our paper we compare three different methods of defining a fox social group but they all gave different answers; sometimes it was just a few individuals which were or were not included in the social group. However, unless we set a threshold of a minimum number of sightings, group estimates were grossly over-estimated because of the number of visitors.
Territories are defined by biologists as ‘defended’ areas, but one of the key things we learnt from this study is how difficult it is to define a fox social group because they also have a community structure. While foxes live in socially-structured groups that share a territory, they also know and interact with their neighbours. Some they ignore (although they are more likely to be challenged in winter), whereas others are greeted literally like long-lost relatives although, despite the enthusiasm of the welcome, in reality they may have been encountered quite recently. These layers of complexity make it very difficult to define a fox social group and, unless you recognise which animals are visitors, possibly regular visitors, you will always over-estimate fox group sizes. The other thing we learnt is that it is completely wrong to suggest that foxes do not have complex social lives: they are every bit as intricate, and structured, as in other social mammals.