Acorns from oaks belonging to the red oak group (Erythrobalanus) are rich in fats and tannins and germinate in the spring. The white oak group (Leucobalanus) has acorns that are less fatty, have less tannins and germinate quickly after maturing and falling. Once germinated, the acorns loose up to 50% of their nutritional value. Here in Northeastern California where we live, the California black oak (Quercus kelloggii) is an example of the red oak group while the white oak group is represented by the Oregon white oak (Quercus garryana).
I was fascinated to read that squirrels use selective strategies between eating acorns and burying them for feeding in winter. Research by Leila Z Hadj-Chikh et. al. and Michael A Steele et. al. reported in the journal, “Animal Behavior” (1995 and 2006 respectively), studied the eastern gray squirrel (Sciurus carolinensis). However, other tree squirrels also appear to use these strategies.
Gray squirrels can tell the difference between red and white oak acorns. In the fall, the squirrels will eat white oak acorns before they germinate while selectively burying red oak acorns. If the gray squirrels do bury white oak acorns (limited supply of reds?) they bite off the embryo before burying the acorn to prevent germination and maintain optimal nutritional value.
Gray squirrels do not hibernate. During early spring when red oak acorns begin to germinate, gray squirrels will dig up their previously buried red acorns, bite off the embryo and then rebury them.
I find it amazing that these rodents can tell the difference between acorn groups and handle each group in a manner that provides maximum food value.
The pictured western gray squirrel (Sciurus griseus) was photographed in North Mountain Park, Ashland OR. Like his eastern cousin, it probably also selectively buries acorns for the winter.