A few animals have digestive systems that can tolerate tannins, or break them down. Unfortunately, we are not among these. If you want to eat a diet heavy in acorns, you too will need to crack open t he acorns and soak them for a while to rinse out the tannins. Native people in California were very good at this. They used rock grinders to break open the acorns, and they would soak the acorns in the streams for many days.
Many animals just go ahead and eat the acorns when they are plentiful.
Any loss of digestive absorption due to tannins may be overcome by a simple increase in the volume of acorns eaten. So, deer, pigs, squirrels, quail, jays and many other native animals eat as many acorns as they can, often leaving them for a few weeks on the ground before they eat them. Each fall, the clackety clatter of Band-tail pigeon wings through yellow sycamore leaves against the cerulean morning sky means these wandering birds have returned to gorge on acorns once again, before they continue to Mexico for the winter. Lives of some animals revolve around acorns. Acorn woodpeckers are such specialists and require acorns to support a stable, resident population.