Dogs descended from wild canids. According to a study published in Science in November 2013, our dogs derived from a wolf population in Europe that has since become extinct. Early dogs never knew where their next meal would come from so the stashing behavior evolved. Their sensitive noses would lead them back to the hiding places when they wanted a snack. Any food item that is in excess of hunger at the time is a surplus that must be saved and not wasted.
Because of their ancestral background, burying or hiding bones and other items is a typical dog behavior, like sniffing and tail-wagging. Just like the wolf that they decended from, their behavior is instinctual and goes back millions of years. It’s a food-saving technique that all dogs today are born having an instinct for, just as their wolf ancestors were. Before being domesticated, this was often a necessary behavior for dogs/wolves to ensure that they’d have adequate nutrition at times when food was scarce.
Even today, canines in the wild (such as foxes) will kill a small animal, feed on it until only the bones remain, then bury the bones to hide them from other animals looking for food. If their next hunt isn’t successful, they can return to the hiding spot and feed on the leftover bones from the previous hunt. The marrow from bones is rich in nutrients and will usually be sufficient nourishment until the next successful hunting expedition.
You might wonder why dogs may also hide their plastic chew toys, which obviously have no nutritional value. The reason is that, initially, dogs don’t realize that the toy is not food, and their instincts lead them to hide the toy when they’re not chewing on it, hoarding it as if it were spare food. A difference between domesticated and wild canines is that domesticated dogs don’t generally retrieve items they’ve hidden or buried, since they are consistently fed and don’t need to return for the hidden item.
The first time I witnessed this hiding the food trait in my dog is when I gave him a marrow bone outside. He only held it for a minute in his mouth, went to the base of a large tree and began to dig a hole. Since he is not a digger by nature (not destructive to the flower beds or yard) I watched, fascinated, as he dug his hole and drop his bone in. He immediately used his nose to cover it up, pushing the dirt back over the bone. He then came right back to where I was sitting on the patio, obviously pleased with himself and wanted to be petted. I brushed all the dirt from his nose and said “Well I guess that was a waste of money”! Since then, he has performed this ritual twice so I don’t give him those kind of bones outside anymore—however, it was highly entertaining!