Many subtle interactions take place between carnivores living in the same area and the result can be that one species displaces (i.e. reduces the number of, or forces out altogether) another – this is called competitive displacement or competitive exclusion, according to the extent of the impact. Essentially when two species are competing for the same resources (food, shelter, space, etc.), one is often better at it than the other and the result is often that the “winner” stays and the “loser” goes. Several such competitive interactions are known for Red foxes; in some cases the foxes are the winners and in others they lose.
In his 1986 book Running with the Fox, David Macdonald recounted trials where Red and Arctic foxes (Vulpes lagopus) were released from fur farms on to various islands, from the Aleutians to the Alexander Archipelago, and left to fend for themselves. It soon became apparent that the two species could not be kept on the same island as the Reds invariably displaced the Arctics and, in one instance, Macdonald described how a single male Red apparently killed all the Arctic foxes on one small island during 1886.
More recently, a team of Swedish biologists found that Red and Arctic foxes were sympatric (had overlapping ranges) during the winter, but allopatric (used separate ranges) in summer, when the latter moved to higher altitudes to breed – they suggest that Arctics may risk coming across a Red fox during the winter when searching for food, but cannot risk the danger during the summer when they have cubs. Indeed, in a paper to the journal Polar Biology, Lomonosov Moscow State University zoologist Anna Rodnikova and six colleagues described the takeover of an Arctic fox breeding den along Russia’s Erkutayakha River by a Red fox in 2007.
The Red fox approached the den and lay down, while the Arctic vixen sat at the entrance barking. Eventually the Red fox moved closer, forcing the vixen to abandon her cubs and move away from the den. There was no indication that the Red fox, which appeared in poor condition, killed the Arctic cubs and the authors believe that the cubs hid in one of the chambers until they had an opportunity to escape. The Arctic vixen made no attempt to fight the intruder.
In a short paper to the journal Arctic in 2006, Nathan Pamperin and co-workers described the killing of an Arctic fox by a Red fox on northern Alaska's Prudhoe Bay Oilfield during November 2004. The video footage showed a Red fox chasing an Arctic fox, the two briefly fought and then the Red bit the neck of the Arctic and shook it violently; it then carried the body off to an undisturbed site and began biting at the back of the neck around the shoulders, apparently trying to open the carcass. Over the subsequent days, it appears that the fox (or other foxes) partially consumed the carcass.
Recently, scientists have raised concerns that the range expansion of Red foxes into southern parts of the Arctic tundra could lead to a reduction in Arctic fox populations. Indeed, there are some data suggesting that Red foxes can suppress the recovery of Arctic fox populations and may even set the southern limit of geographical distribution for the species. In the early 1900s, the Swedish Arctic fox population crashed in response to over-hunting and, despite legal protection in 1928, the population never recovered; it has been suggested that predation by Red foxes was the reason. In January 2013, the BBC News website ran a story about how Arctic fox sightings hit an all-time low in northern Canada during the winter of 2012/2013 – a response, it is suggested, to a surge in the number of Red foxes in the Hudson Bay area. The Wildlife Photographer of the Year 2015 competition was won by Canadian photographer Don Gutoski with his photo “A tale of two foxes”, showing a Red fox eating an Arctic fox at Cape Churchill.
In addition to direct displacement of Arctic foxes, concerns were recently raised about the two species hybridizing following the discovery of an Arctic fox with a reddish coat. During February 2013, an Inuk hunter shot “an Arctic-like fox exhibiting an unusual reddish winter coat” in the vicinity of Igloolik in Canada’s Nunavut territory. The pelt was subjected to multi-genetic analysis by a team led by Glenn Yannic at the Universite´ de Moncton in Canada. The results were published in a paper to Polar Biology in 2017 and clearly demonstrate that this animal was pure Arctic fox displaying an unusual coat colour, the genetic foundations for which have yet to be determined.
Weasels & martens
Writing in the Journal of Wildlife Management in October 1952, Roger Lantham of the Pennsylvanian Game Commission described how “foxes will kill weasels at every opportunity even though they do not find them particularly palatable”. Lantham also reviewed the bounty records from the state for 1930 to 1951, assessing how the number of trapped foxes fluctuated with the number of weasels caught. He observed a decline in the number of weasels caught after the fox population erupted around 1935 and, while bounty records can be unreliable sources of population information, Lantham’s analysis revealed an interesting apparent correlation between the two predators, in that counties with the highest weasel captures (i.e. >500 per year) were those with fox:weasel ratios of about 1:1. Counties with ratios of 9:1 reported <100 weasels caught per year. Overall, Lantham concluded:
“From the evidence presented, it appears logical to assume that where foxes are numerous in Pennsylvania they are capable of reducing and controlling the resident weasel population.”
In the early 1970s, wardens on the North Holland Dune Reserve in the north-west of Amsterdam started noticing a decline in the number of stoats (Mustela erminea), a once abundant species on the dunes, and, in the annual report of the Provinciaal Waterleidingbedrijf van Noord-Holland, published in 1975, it was noted that:
“According to the game wardens the foxes have destroyed virtually all the stoats and weasels, and possibly the polecats and young feral cats too”
In his meticulous review of the situation, published in the journal Lutra in 1990, Jaap Mulder considered it most probable that the arrival of foxes on the reserve, sightings of which began increasing significantly in 1968, was the most likely explanation. According to Mulder, two stoats and about ten polecats were found dead in the reserve between 1978 and 1985 that, on examination, showed punctures in the chest region or the skull characteristic of a fox bite. By 1985, the stoat was extinct from virtually the entire dune system.
In a 1995 paper to the journal Annales Zoologici Fennici, Swedish biologist Erik Lindström presented evidence that foxes could be a significant predator of pine martens (Martes martes) and that high fox numbers can cause declines in marten abundance. More recently another Swedish team, led by biologist Nils Carlsson, found evidence that, in areas of Sweden where fox populations had crashed following a mange epidemic, American mink (Mustela vison) populations had increased. In their 2010 paper to Biological Invasions, they noted:
“We suggest that the mink's population tripling was caused by a drastic decline in red fox populations, which caused terrestrial prey to increase. Later recovery of the fox populations reversed the trend and caused the mink population's recent decline.”
In other words, the foxes weren't actively predating the mink, as Lindström found with pine martens, but rather they were competitively excluding them. When the foxes died off, the mink had access to the foxes' food supply and their population increased.
Similarly, in a 2001 paper to the journal Oikos, a team of Swedish biologists led by Tarja Oksanen at Umeå University discussed the population regulation and cycling of carnivores and herbivores in the Northern Hemisphere. Oksanen and her colleagues suggested that winters with little snow cover may improve the hunting efficiency of generalist predators, such as the Red fox, at the expense of more specialist predators, such as the least weasel (Mustela nivalis), and may consequently alter the population dynamics of the voles on which they both feed.
Not all interactions with carnivores end in favour of the fox. It is widely known that large carnivores—e.g. Eurasian lynx (Lynx lynx), grey wolves (Canis lupus), coyotes (Canis latrans), etc.—can displace foxes; in Britain even domestic dogs have been associated with deterring foxes from some urban areas. Coyotes and lynx seem especially intolerant of foxes and have been implicated in changes in their distribution and declines in their population in some regions (see QA). Recently it has been suggested that promoting the recolonisation of Australia by the dingo (Canis lupus dingo) could similarly serve to reduce or control Red fox populations there. Dingoes are large dogs native to Australia and there is evidence that they both target many of the same prey items that Red foxes hunt and kill foxes.
In a paper to Global Ecology and Biogeography in 2011, a team of Australian biologists led by Mike Letnic at the University of Western Sydney presented data on dingo and Red fox abundance in mainland Australia based on bounty schemes and field tracking. The data revealed consistently negative associations between abundance indices of these species – in other words, foxes appeared to be avoiding areas inhabited by dingoes. Indeed, foxes were most abundant in western New South Wales, where rabbits were plentiful and dingoes rare. More recent studies have found foxes to be more nervous in areas treated with dingo scent and that the presence of dingos results in fewer foxes and simultaneously more medium-sized ground dwelling mammals, such as the rufous rat-kangaroo (Aepyprymnus rufescens) and brown bandicoots (Isoodon macrourus). It is suggested that dingoes could help reduce fox populations across Australia and thus offer potential relief to some of the continent’s native mammals that have declined since foxes were introduced (see QA).
Closer to home, some studies have suggested that foxes may be displaced by European badgers (Meles meles). Field observations have long suggested that, when the two species meet, badgers are dominant to foxes, even though they may sometimes share setts or feed together in gardens. In 2004 the WildCRU team at Oxford University published some observations of badgers and foxes at artificial feeding sites in Wytham Woods. The results showed that the badgers were clearly dominant over foxes, fed in longer bouts and were less vigilant while feeding than foxes. Indeed, writing in their paper to the Journal of Zoology, the biologists explained:
“Aggression between badgers and foxes was exclusively in the form of a badger charging towards a fox and swiftly displacing it. No instance of physical contact or injury was observed, and foxes never charged badgers.”
Foxes were, it seems, significantly more vigilant than badgers at feeding sites and the duration of their vigilance was associated with the number of badgers present (i.e. the more badgers around, the longer the fox was alert for). When the foxes arrived at the feeding site they would either choose an unoccupied feeder or wait for the badger to leave, while badgers commonly walked up and shoved foxes off feeders. The badgers rarely tried to chase each other away from a feeder, while foxes frequently bolted when charged by a badger – it appears a badger is less intimidated by another badger than a fox is. Despite being wary of them, foxes were often seen in the presence of badgers and the authors suggest they may even follow badgers to good feeding grounds.
A fox's response to the presence of a badger is likely to be individual-specific, with some willing to take bigger risks than others. Indeed, I have seen several photos of foxes and badgers feeding, apparently convivially, from the same dish and, in her 2000 book A New Forest Fox Family, Thelma Clarke wrote:
“There clustered around the chips and general scraps were five badgers and to complete the picture, amongst the busy mass of grey was a thin streak of gingery brown. Squeezed in between all those sturdy bodies making sure of her share was the little vixen I called, for good reason, 'The Cheeky One'.”
Clarke mentions that, although foxes generally have a healthy respect for badgers, she saw a fox stand up to a badger on one occasion. Unfortunately, she does not recount the event. Outside of the UK, there is at least one report of a fox harassing an American badger (Taxidea taxus) for access to a carcass. In a paper to the Journal of Mammalogy during 1963 Minnesota-based biologist Edmund Hibbard described how a fox repeatedly lured the badger away from a sheep carcass. The fox would approach the feeding badger, which would break away to chase the encroaching fox. The fox, being the faster of the two, was able to run around behind the badger and arrive back at the carcass in time to take a few mouthfuls before the slower badger came back. Hibbard wrote:
“It worked only because the nimble fox apparently “knew” that he could only entice the badger away by staying just barely out of the badger’s reach.”
The fact that foxes and badgers feed on many of the same prey items is probably part of the reason why fox populations appear to increase in the absence of badgers, as implied by data collected during the Randomised Badger Culling Trial (RBCT) in England between 2000 and 2006. During this time, badger numbers were reduced in a bid to assess what impact this would have on the incidence of bovine tuberculosis outbreaks in cattle herds. Upon analysing some of the RBCT data, a team of biologists led by Iain Trewby at the Central Science Laboratory in York found that, where badgers were culled, average fox densities increased by about two-fold over those areas where badgers weren’t. Writing in the journal Biology Letters during 2008, Trewby and his colleagues suggest that killing badgers led to more food being available to foxes and thus their populations were able to increase – this is known as competitive release, or sometimes mesopredator release. It is important to recognise that this is only one study based around a comparatively small data set, but it provides some interesting food for thought on a topic that warrants further study.