But not all acorns are created equal — or eaten equally in fall and spring. Oaks belong to one of two groups: white (white, swamp white, bur, chinquapin) and red (northern red, pin, black). Of the two, white oak acorns have fewer tannins. This makes them more palatable (and preferable) to wildlife. White oak acorns also germinate more quickly, which means they start to convert their fats and carbohydrates into sprouts earlier in the growing season. As a result, animals may eat a mix of white and red in fall, but in spring, when many of the tastier white oak acorns have already been consumed and those that remain are starting to sprout, animals may rely more on red.
Migrating songbirds are another guild that depends on oaks for food, although not for the acorns. Over 500 species of insects live and feed on oaks; other widely planted trees only support a handful. Because of this disparity, you’re more likely to attract migrating birds to your yard with oaks than, say, maples. Oaks’ catered bug buffets allow Wilson’s warblers, American redstarts, common yellowthroats and other migrants to find food faster, saving time and energy for their long journeys ahead.
In addition to being a critical source of food, oak trees offer valuable shelter. Natural cavities can form in any tree, but larger species, oaks included, can support larger cavities without detriment to the trees themselves. This means more sizes and species of wildlife are able to claim squatter’s rights. Red-headed woodpeckers, identified as in greatest need of conservation by the Illinois Wildlife Action Plan, rely on cavities to raise their young as do eastern bluebirds and southern flying squirrels. Because they all readily nest in oaks, adding oaks to your yard can make all three great additions to your wildlife watch list.
Even an oak tree’s leaves are superior when it comes to habitat. Leaves on deciduous trees “senesce” in fall, which means they die and dry up. On many trees the leaves soon drop, but the browning leaves on some oaks remain on the branches through winter. This gives smaller tree-dwelling creatures cover from predators at a time when cover is scarce. When an oak does drop it leaves, they decay more slowly and remain in the environment longer than others, creating protected areas for mice, snakes, insects and other animals that shelter on the ground.
Because oak leaves take longer to decay than those from other trees, they provide valuable cover and camouflage for ground-dwelling animals, such as American toads. Image by Will Parson/CC BY NC 2.0
There’s a Greek proverb that states, “A society grows great when old men plant trees whose shade they know they shall never sit in.” Planting an oak tree in your backyard will not only enrich your quality of life today but also welcome and maintain healthy populations of wildlife for years to come.