Acorns in the deer's diet

Mark has really kept on top of the deer deterrents this summer, and we haven't had a single incursion in months.  In past years, deer damage was already starting to get extreme by late October, but it's possible that wild foods are especially abundant this year, keeping the deer well fed in the woods and out of the garden.  As always, it's a lot easier to figure out why the deer got into the garden than to try to decipher which factors are keeping them out, but I can't help pondering the issue.

Of all the natural foods, acorns are perhaps the most important in a deer's fall diet.  Since oak trees mast --- produce few nuts most years, then all gang up and produce a bumper crop during certain years --- it's unsurprising that studies have shown varying percentages of acorns in a deer's diet.  A quick search of the web turns up figures ranging from 20% to 75% for acorns' contribution to the diet of a white-tailed deer.

Not all acorns are created equal, though.  Oaks can be divided into two large groups: the white oaks, including white oak, chestnut oak, and others with rounded lobes on their leaves; and the red oaks, including red oak, black oak, scarlet oak, and others with pointy lobes on their leaves. 

Although you might have a hard time identifying the acorn you find on the forest floor, a deer is much more discerning.  Acorns in the white oak group are sweet, with low concentrations of bitter tannins, so they are a preferred food early in the fall.  As you can see from this photo, though, white oak acorns make up for their tastiness by sprouting quickly, so by late October, there are often few unsprouted white oak acorns around for deer to chomp on.

That's when red oak acorns shine.  With their bitter nuts, red oaks figure they can wait until spring to sprout, and the tannins do deter many seed predators.  But by late fall, deer are getting hungry, so they turn to the red oak acorns.

Since red and white oaks tend to produce bumper crops during different years, deer often end up hungry during either the early fall or late fall, but in our neck of the woods, both red and white oak acorns are currently common on the ground.  Clearly, this double mast year has kept the deer very well fed.