Red oak acorns have a higher fat and tannin content. Tannins are bitter tasting chemicals that can interfere with digestion. Since all oaks contain tannins in their leaves and acorns, those with higher amounts of tannin are less attractive to herbivores. Squirrels bury red oak acorns in the forest floor where rain and snow gradually lessen the tannin content over winter. In spring the nuts are fit to eat and also able to sprout.
Wood ducks forage heavily on white oak acorns before beginning their fall migration.
Deer also favor the nutritious nuts. Acorns are quickly converted to energy-producing fat for both animal species. Recent heavy acorn crops coupled with mild winters have led to an increase in local wild turkey populations. Early explorers in America told of huge flocks of passenger pigeons that stripped oak trees of nuts in a matter of minutes. By the end of the 1800s the cutting of forests to make way for farmers had so reduced the mast supply that turkey and pigeon populations plummeted.