Acorn: Encyclopedia II - Acorn - Nutrition

Acorn - Nutrition

Acorns are thus 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 humans 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 flavour, 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 mouldy easily and must be carefully stored. Acorns are also sometimes prepared as a massage oil.

Acorn - Acorn dispersal agents

Acorns, being too heavy to blow in wind, do not fall far from the tree at maturity. Because of this, oaks depends on seed dispersal agents to move the acorns beyond the canopy of the mother tree and into an environment in which they can germinate and find access to adequate water, sunlight and soil nutrients, ideally a minimum of 20-30 m from the parent tree. Many acorn predators eat unripe acorns on the tree or ripe acorns from the ground, with no reproductive benefit to the oak. However, some acorn predators also serve as seed dispersal agents. Jays and squirrels that scatter-hoard acorns in caches for future use, effectively plant acorns in a variety of locations in which it is possible for them to germinate and thrive. Although jays and squirrels retain remarkably large mental maps of cache locations and return to consume them, the odd acorn may be lost, or a jay or squirrel may die before consuming all of its stores. A small number of acorns manage to germinate and survive, producing the next generation of oaks.

Scatter-hoarding behaviour depends on jays and squirrels associating with plants that provide good packets of food that are nutritionally valuable, but not too big for the dispersal agent to handle. The beak sizes of jays determine how large acorns may get before jays ignore them.

Acorns germinate on different schedules, depending on their place in the oak family. Once acorns sprout, they are less nutritious, as the seed tissue converts to the indigestible lignins that form the root.

Adapted from the Wikipedia article "Nutrition", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki