Lately when I’ve walked in the woods I felt like I should be wearing a hard hat. Acorns are raining down around us, thunking on the ground, pinging on metal roofs and causing my chickens to think the sky is falling. Yet for some birds and mammals the acorns are manna from heaven. These seeds from the oak trees are packed with carbohydrates, protein, fats and minerals that provide nutrition now and through the winter for a wide variety of wildlife species.
In our area, the most common oak trees are northern red oak and white oak, though black and pin oak can be found as well. Distinguishing between the acorns from these species is not hard. The white oak acorn is oblong, 0.5 to 0.8 inches long, and has a warty, deep, bowl-like cap.
The red oak acorn is slightly larger, 0.8 to 1 inch long with a flat, saucer-like cap.
The black oak acorns are similar in size and shape to white oak, but the cap is more scaly than warty.
Pin oaks have acorns that are nearly round, only 0.5 inches across, with a thin, scaly cap.
If you notice the leaves on the trees, they are also quite distinctive. White oak leaves have rounded lobes while the others have pointed lobes. Pin oak leaves have deep cuts between the lobes, so the leaves look as though they have fingers.
The animals that forage for and feed on acorns seem to be able to tell them apart as well. White oak seeds are preferred because they have a thinner shell and less tannic acid. Early American Indians knew this too and preferred the less bitter white oak to red oak when using acorns for flour. They thoroughly rinsed the nuts to remove the tannins and reduce the bitter taste.
Collecting enough of them before the animals got them must have been quite a challenge. It is much more common to find empty caps of white oak acorns than it is to find intact nuts. They seem to get scooped up as quickly as they hit the ground.
Most people are aware that squirrels (primarily gray squirrels) and chipmunks are big consumers of acorns. However, acorns make up a sizable portion of the diet of other mammals such as white-tailed deer, bears and raccoons. Birds including wood ducks, wild turkeys, blue jays, white breasted nuthatches and common grackles also rely on them.
When you find a pile of acorn shells or caps, its fun to try to determine which consumer left behind the scraps. Crushed outer shells are clues that deer have been chewing on the nuts to get to the inner meat. Wild turkeys eat the whole thing, letting their gizzard do the grinding. The best sign of their activity is scratched up leaves under the oak trees. Squirrels and chipmunks peel the shells; the size of the peelings indicates which rodent has been eating (smaller ones left by chipmunks). Of course, chipmunks also just grab and go, taking the nuts into their underground burrows to be eaten in the winter when they are hiding from the snow and cold. They can store hundreds of acorns in underground caches.
The moving, burying, and storing of nuts is beneficial for the oaks. Acorns must be buried in order to germinate, or they will dry out. A large percentage of nuts that get stashed in the ground are forgotten by the foragers. These are the seeds that will germinate and produce future oak trees. This of course is the reason why acorns are produced.
To insure that some acorns actually survive to produce new trees, oaks and other nut bearing or "mast" trees produce their seeds in cycles. Every few years a "mast year" occurs, and the habitat is saturated with an over abundance of seeds so that the predators can’t possibly consume them all.
The occurrence of a mast year is hard to predict. Weather is likely a factor. There are other influences that are not completely understood. One theory is that the trees in a particular area "communicate" chemically about when it is time to over produce, so that they are all on the same schedule.
This year does not seem to be a mast year, but there are still plenty of acorn bombs dropping towards our heads, so be careful as you get out and share the season with the nut hunters.