We have seen that fox diet varies according to location, season, habitat and weather/climate, but what about sex and age? Do males eat different foods to females? Do cubs eat different prey to their parents? The succinct answers are: “no” and “yes”, respectively. Most dietetic studies simply look at remains in fox scat, which makes it impossible to assess the effect of sex (generally age, too), but studies based on stomach contents have typically failed to find any differences between dogs and vixens. That said, there are some data (largely cranial and musculature measurements) to suggest that dogs are capable of taking larger prey than vixens, and may do so in some regions.
A recent study of foxes in Finland by Suvi Viranta and Kaarina Kauhala has suggested that, since the introduction of the invasive Raccoon dog (Nyctereutes procyonoides), vixens have taken to catching larger prey than before. The authors suggest that increased competition from the Raccoon dog may have driven the foxes to a more ‘hyper-carnivorous’ diet (i.e. taking more large prey, such as hares and deer fawns). Interestingly, no change was observed in the diet of the dog foxes, suggesting that they were already taking larger prey than vixens.
Many fox watchers have observed that the diet of cubs often differs considerably from that of the adults feeding them. Jan Englund was among the first to record this phenomenon during her three year study on the diet of fox cubs (based on stomach contents) in various parts of Sweden. Englund found that mammals (mainly voles and hares) and birds (particularly gamebirds, poultry and thrushes) were important in all areas, with much greater variability found for deer kids, cats, eggs, fish, insects and reptiles. Garbage and scavenge in the diet ranged from less than 1% to about 20% of the cubs’ diets and, in all areas, they increased the fruit eaten as the summer progressed. Most interestingly, Englund observed that, when out hunting, the adults would bring large prey items, such as hares, back to the cubs, while there was a greater tendency to eat small mammals (voles) themselves.
Studies of food remains at cubbing earths suggest a similar trend, with plenty of larger prey remains scattered around (although voles are usually eaten whole, leaving little evidence, and so could be underestimated by such studies). Raymond Hewson, during his studies on the foxes of the Scottish highlands, found that while adults in the west and north-west commonly ate field voles, they preferentially brought lamb carcasses back to the earth for the cubs. Erik Lindström, working in Sweden, saw a similar picture, although he found that voles were brought back more often when they were in abundance locally, with larger prey brought in when voles were in short supply. Lindström concluded that foxes were applying what ecologists call the “central foraging theory”. The CFT predicts that a single prey loader (i.e. an animal that hunts for one prey item at a time) should eat smaller prey on the spot and bring larger/bulkier items back to the young in the den.
Finally there is the question of what the cubs start eating when they’re independent. Many of us still enjoy childhood favourite meals—those foods we were brought up eating—even though our palates may since have matured or diversified. There are some interesting accounts of young mammals growing up to preferentially take the species fed to them by their parents. In the early 1970s, for example, Raimund Apfelbach found that captive polecats (Mustela putorius) learnt to recognise what to eat based on the smell – familiar smelling food (i.e. that they were fed by their parents) elicited a hunting response, while unfamiliar smelling prey did not.
I’m not aware of any similar empirical data for foxes, but there is some intriguing circumstantial evidence. There is an old adage, for example, that gamekeepers will leave a fox family being raised on rodents alone because the young will grow up to eat rodents, while cubs being fed birds would be destroyed. Similarly, observations by Erik Nyholm of foxes on the islands of Kennit and Kuusamo in the Gulf of Bothnia (northern Baltic Sea) found they would seldom touch other prey if fed on fresh Snowshoe hare (Lepus americanus) meat.
Huw Gwyn Lloyd had much the same experience and, in his 1980 The Red Fox, he recounted how his captive foxes were raised on quail and would rather go hungry than eat either rabbit or dog food if quail was unavailable. Finally, in My Life with Foxes, Eric Ashby wrote:
“There is a theory that there are two kinds of fox: fur and feather. Foxes learn what to eat what their mothers give them.”