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A crow landed on mowed grass with a crust in its beak. It buried the crust in grass and then did this four more times. What was it doing?

Sent in by Burt Jervis, Wythall, near Birmingham

This is interesting behaviour indeed. What the crow was doing was caching food.

Many animals cache food, with some going to greater effort than others. A prime example is the acorn woodpecker in North America, which is famous for drilling holes in tree trunks in the autumn, and then wedging acorns in each as it builds up its winter larder. Should you ever put out loose peanuts on a bird table, you will soon find that they are carried away by coal tits, nuthatches, woodpeckers and squirrels, who bury them in the ground or otherwise hide them in vegetation to store them for future use. 

A variable amount of these stashes are never found again. For instance, a coal tit simply hides food items randomly in a given area. It will remember the general area where its store is, but it will have to search hard to find any of the seeds or nuts it knows are somewhere out there.

A crow is far more methodical about caching food. It too has a favourite general area where it stores food, but instead of simply burying the food item, it will place a leaf, twig, bit of grass or some other item it is likely to remember on top of the food as a marker. If you watch the bird carefully as it is covering the food item, you will see that it tilts its head sideways, so that it can look at the marker on the hiding place with one eye and the surroundings with the other. In effect, it is creating a mental image of where it hid the piece of food so that it has a better chance of finding it at a later time when it wants to eat it.

Caching can be either temporary storage or to build up a food store for the winter. The bread crusts the crow you describe was hiding will no doubt have been intended for short-term storage. I guess the bird had found all the crusts on a bird table, and, unable to eat them all before other birds were on the scene for their share, it chose to carry them away, one at a time, and hide them so it could later eat the whole lot at its leisure.

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