Squirrels have no idea where they have buried their nuts. Other animals do: for them, the search is also memory training.
Cute, but forgetful: the squirrel Photo: dpa
Recently, a silver badger in the U.S. buried a dead calf in the ground for five days. In a video posted online by the University of Utah, he can be seen doing just that. Judging his appetite correctly, the badger came to the conclusion that he had better hide the calf if he wanted to secure it as a food source for longer. At least from the vultures, which are still common in the U.S., he had thus brought "his" calf to safety.
Animals usually hide objects in connection with feeding. The U.S. silver badger can be considered exemplary in this context. Even vultures, which like turkey vultures are very good at smelling very fine decomposition particles miles away, will not be able to dig up the buried calf.
With this example, a few problems of animal hiding are already literally in view: Even when animals hide food to keep it safe from other interested parties, they must always expect to be observed in their game of hide-and-seek.
This also applies to crocodiles when they bury a wildebeest they have just caught and only half eaten in the mud of the river bank in the Serengeti. And it is true for the female lizards, which bury their eggs in the warm sand on the banks of rivers and ponds.
Crocodiles, monitor lizards, storks
Because laying eggs in a self-dug depression in the sand is very unsafe, female Nile crocodiles stay close to the brood from the time the eggs are laid until the young hatch. Whereby, whenever they, possibly overheated, briefly go into the water to cool down, it immediately becomes clear why they should actually guard their nests. Most of the time the crocodile is not yet completely gone, when monitor lizards already come out of the undergrowth of the gallery forest and search for the eggs.
Apparently attracted by the monitor lizards, two storks also fly in and just stare at the monitor lizards. Monitor lizards, if not prevented from doing so, dig up the crocodile eggs and eat them. For the storks, with about a hundred eggs, there are still some left.
So hiding is never a sure thing in the animal kingdom. Thieves or fellow eaters lurk everywhere. This is especially true when the food smells particularly intense, like the calf of the silver badger. Then the hiding place is not secure from other carnivores and scavengers who, like foxes or wolves, are able not only to smell the carcass but also to dig it up.
Besides the disadvantages of being smelled by others, there is also an advantage for hiders like the badger: He doesn’t have to remember the spot where he buried his stash so precisely. He can simply rely on his nose. A behavior that every dog owner with several flower pots in the apartment knows well. Dogs hide their prey, their gnawed-off leftover bones in different places and then look for them again with their snout in the flowerpot soil – and not with pinpoint digging.
The fact that you have to remember the place where you hid something if you want to find your hiding place again yourself becomes a problem, however, if the hidden object does not smell. Plant seeds, for example. They are among the most frequently hidden objects by animals, which is also related to their long shelf life and concentrated food quality.
Broadly speaking, there are two strategies for dealing with seed hiding places. One of them is exemplified by squirrels. They bury their nuts in autumn in all sorts of places in the ground around the trees where they live.
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They don’t remember the exact places. They only remember the approximate space where they buried something. As seemingly confused and hardly purposeful as they hide, they also try to dig out the nuts again. Often a lot of earth is moved in the process, without the yield going beyond a single nut.
The exact opposite of this are corvids and among them especially the jays. If you have a jay in a backyard with a balcony where there are flower boxes, you can observe that jays – but also crows – hide all sorts of things there, from dry spaghetti to acorns. What’s amazing about this is the jays’ memory capacity.
60,000 seeds in 6,000 places
Jays living in the forests hide pine seeds in large numbers in the ground or in rock crevices in widely separated places. It is amazing that they find the hiding places again in winter even when there is a snow cover of more than one meter above them. The jays then shoot head first into the snow and dig their way to the seed.
But the masters among seed hiders known so far are pine jays. A single one of them can hide up to 60,000 seeds in 6,000 different places and find them again in winter. The jays remember not only the hiding places, but also which seed they hid when and in which place, so that they can dig it out again just in time before it sprouts.
The British neuroscientist and evolutionary biologist Nicky Clayton, who keeps jays in the laboratory for experimental purposes, was able to show that this outstanding memory performance is based primarily on practice. During the seasons when her jays could not hide seeds, they hid all kinds of other small objects such as stones or found plastic stuff. The memory capacity that lets the birds find the right seeds at the right time is kept at a high level by practice on seemingly useless objects such as stones or knickknacks.
Hiding objects is thus often nothing more than a kind of memory training that not only ensures the birds’ survival, but also results in a particularly intense engagement with the conditions of their environment.