Acorns are one of the most important wildlife foods in areas where oaks occur. Creatures that make acorns an important part of their diet include birds such as jays, pigeons, some ducks and several species of woodpeckers. Small mammals that feed on acorns include mice, squirrels and several other rodents. Large mammals such as pigs, bears and deer also consume large amounts of acorns; they may constitute up to 25% of the diet of deer in the autumn. In some of the large oak forests in southwest Europe, pigs are still turned loose in oak groves in the autumn, to fill and fatten themselves on acorns. However, acorns are toxic to some other animals, such as horses.
In some human cultures, acorns once constituted a dietary staple, though they are now generally only a very minor food.
The larvae of some moths and weevils also live in young acorns, consuming the kernels as they develop.
Acorns are attractive to animals because they are large and thus efficiently consumed or cached. Acorns are also rich in nutrients. Percentages vary from species to species, but all acorns contain large amounts of protein, carbohydrates and fats, as well as the minerals calcium, phosphorus and potassium, and the vitamin niacin. Total food energy in an acorn also varies by species, but all compare well with other wild foods and with other nuts.
Acorns also contain bitter tannins, the amount varying with the species. Since tannins, which are plant polyphenols, interfere with an animal's ability to metabolize protein, creatures must adapt in different ways to utilize the nutritional value that acorns contain. Animals may preferentially select acorns that contain fewer tannins. Creatures that cache acorns, such as jays and squirrels, may wait to consume some of these acorns until sufficient groundwater has percolated through them to leach the tannins out. Other animals buffer their acorn diet with other foods. Many insects, birds and mammals metabolize tannins with fewer ill-effects than humans. Several human cultures devised acorn-leaching methods that involved tools, and that could be passed on to their children.
Species of acorn that contain large amounts of tannins are very bitter, astringent, and potentially irritating if eaten raw. This is particularly true of the acorns of red oaks. The acorns of white oaks, being much lower in tannins, are nutty in flavor, which is enhanced if the acorns are given a light roast before grinding. Tannins can be removed by boiling chopped acorns in several changes of water, until water no longer turns brown. Being rich in fat, acorn flour can spoil or get moldy easily and must be carefully stored. Acorns are also sometimes prepared as a massage oil.
So it is not poisonouns.
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