Foxes are extremely possessive of their food and, even at an early age, will defend their catches from other (even more dominant) animals. Food may not, however, be eaten all at once and some may be buried for later retrieval – this process, practiced by many animals, is called caching (pronounced “cash-ing”) and is an inherent behaviour.
Several authors describe watching very young cubs cache food brought back to the earth by their parents and, in Free Spirit, Michael Chambers described how his hand-reared vixen, Ferdi, broke into the pantry while he and his wife were watching TV to demolish a packet of chocolate biscuits, or so they thought. Upon ascending the stairs, a curious crunching sound alerted them to the young vixen having cached the biscuits under the carpet running up the middle of the stairs; two per stair. Most biscuits were intact, suggesting the operation had been carried out with considerable care and precision, despite her never having been taught to cache food.
When an animal chooses to store surplus food there are two main choices it has: it can either store everything together in one place (larder cache), or it can bury everything individually or in small clusters (scatter cache) in different locations. The pros and cons of these are discussed in an associated QA so I won't go into detail here. In a nutshell, though, if you larder cache it makes it easier to recover everything at a later date, but at the same time if someone discovers your hoard you're likely to lose everything. Conversely, if you scatter cache you minimize losses in the event someone else finds it, but you must remember the location of each cache. Foxes, it seems, show a general tendency towards scatter caching, although there are exceptions.
The question, though, is why should a fox want to cache anything? Ultimately, foxes aren't fortune-tellers; they cannot see into the future and know whether they'll hunt successfully tomorrow. Consequently, foxes hedge their bets. Seldom will they pass up an opportunity to hunt and if hunger doesn't drive them to eat the prize straight away the logical response is to put it somewhere safe for later, when pickings may be slim. It's no different from us going to the supermarket once a week to stock up with food. In instances where a fox's predatory instinct is over-stimulated, such as the oft-cited fox in the chicken coop example, caching helps make the most of the valuable resource of dead birds, if the fox get the opportunity to remove them. The subject of surplus killing and the various explanations for the behaviour are covered in an associated QA, so I won't delve any further into the topic here.
Caching tends to involve a fox digging a hole with its front paws, placing the object into it and then pushing the soil and vegetation on top with the snout. In urban and suburban areas, these holes tend to be in flower borders, pots and in lawns, and while filming for the series Dogs in the Wild, which aired in December 2022, the BBC camera crew observed foxes in London caching leftovers in the bonnets of parked cars. The suggestion is that cars parked in urban areas tend to move relatively infrequently and therefore make reasonably safe caching sites.
Observations of wild and captive foxes have shown that the desire to cache food appears at about six weeks old and that the appearance of the cache varies with age (adults being more proficient at concealing a cache than cubs) and how hungry the fox is - satiated foxes tend to make rather haphazard caches. An item may be cached even when the fox is still hungry and it seems that preferred foods are more likely to be eaten on the spot, while less palatable morsels are cached. Various other factors, including season, age, social status and whether the fox thinks it's being watched may also have an impact on caching behaviour.
During the spring and summer, when a vixen is rearing cubs, less palatable food items (that might normally have been ignored) are cached as an insurance policy. Furthermore, Macdonald also observed that when surrounded by other adults (during which squabbling was likely) foxes were more likely to cache food, including items that might otherwise have been avoided. This ties in with my observations of a group of foxes feeding in Guildford, West Sussex; subordinate animals (as determined by submissive behaviour towards others in the group) would skulk into the area, grab food and disappear into the darkness, returning a few seconds later for more. The period that the foxes were gone was, in my opinion, too brief to permit consumption of the items taken, suggesting to me that the items were being cached close by. In Free Spirit, Michael Chambers noted how Ferdi would never cache food if Mike's dogs were watching. If the vixen left the garden with her prize and was followed by one of the dogs or cats she would return carrying it—only when she snuck away unseen would she return without the food.
Broadly-speaking, foxes recover their caches within a day-or-so, although Tinbergen found that some of the gull eggs cached on his dune study site were recovered up to two months later. (Studies on Arctic foxes in Russia suggest that snow goose eggs buried in the ground have lost only 8% of their nutritional value two months later, suggesting caching is a good strategy for such robust food items.) In Bristol, Stephen Harris found that most caches were excavated on the following night, with studies elsewhere showing that almost all are recovered within a week of burial. One fox's cache may occasionally be raided by another fox (or other species, such as badgers), although the 'cacher' is often very careful at concealing the cache site—even to the extent of walking backwards brushing paw prints away as they go—and David Macdonald found that other foxes were generally unsuccessful at finding caches that weren't their own. At the same time, in 2019 one of my trail cameras in Buckinghamshire recorded a badger recover a cache made by a fox earlier in the evening (see below). Highly-prized food items may be cached more diligently than lower-value ones. At the same time, several naturalists have noted how well-fed foxes tend to be rather “sloppy” when it comes to caching, leaving wings and legs protruding and sometimes not even bothering to cover the food! Interestingly, toxoplasmosis may also affect a fox's caching behaviour; reducing/removing scent-marking behaviour and making them more tolerant of cache pilfering.
Macdonald observed that foxes may dig up and relocate a cache if they think someone's wise to its location and some particularly fascinating observations from naturalist and fox rehabilitator Kelly Kilfeather suggests that, like squirrels and some corvids, foxes can be very sneaky in order to maintain the security of their caches. Kelly described to me behaviour observed between two foxes, a dominant male “Gus” and subordinate “Sage”, visiting her allotment. Gus made a habit of raiding caches made by Sage on a daily basis, within a couple of hours of it having been buried, until a highly-prized sausage was provided. Kelly told me:
“... one day, Sage cached one of these treats in front of me… nice cooked sausage… and he spent ages and ages covering it and patting it over, until visibly you would have no idea it was there… and then he did something that shocked me. He went and took a bit of the tinned food, which was mixed with anchovy, so it really whiffed… and he took a tiny morsel of it, dug a hole 1ft from where the sausage was, and dropped it into the hole. Did a half hearted nose push of the dirt to cover it, and then spent ages, rubbing his muzzle all over the ground, all around the hole and all around where the sausage was hidden…. and off he went. Gus came… sniffed around where the anchovy scent was, found the badly hidden morsel, ate it, and went off on his way… the sausage never got spotted.
Gus thought he'd found everything there was to be found and Sage's dummy cache had fooled him. And the weird thing is, Sage carried on making rubbish caches everywhere and I can't help think now, after seeing the cleverness of that little ruse, that he was playing the part of 'useful idiot' for Gus… that if the dominant fox thought he had a handy regular supply of rubbish caches made by this sub fox, he'd be more tolerant…. and he did become more tolerant! Sage managed to stick around all year.”
When it comes to relocating a cache, it seems that foxes rely heavily on their memory, rather than just remembering the rough area (based on landmarks) and then letting their nose lead them to the exact spot. Macdonald found that when he cached another mouse within three metres (10 ft) of his vixen's cache she found only about 20% of them (but recovered 90% of her own caches), and when he dug up her cache and moved it one metre (3 ft) away she only found one-quarter of them. If she was relying on her nose for the last stages of the recovery she should surely have found both the additional and transplanted caches.
Several authors have noted how foxes not only seem to remember what is in a particular cache, but seldom return to an empty cache. It is possible that foxes remember which caches they have excavated and which they haven't, but during his studies on the boreal forest foxes of Canada, David Henry proposed an alternative explanation. Henry suggested that foxes urinate on caches once they've excavated the contents and know that the smell of urine means there's no food left and it's not worth wasting time digging—in other words, the foxes use this scent-marking as a kind of cache book-keeping system. Henry noted that, for the most part the system seemed to work, but in some cases the smell of food must have been so strong that the fox dug anyway.