Evidently in some parts of the U.S. there are no acorns to be found, at all:
The idea seemed too crazy to Rod Simmons, a measured, careful field botanist. Naturalists in Arlington County couldn't find any acorns. None. No hickory nuts, either. Then he went out to look for himself. He came up with nothing. Nothing crunched underfoot. Nothing hit him on the head.
Then calls started coming in about crazy squirrels. Starving, skinny squirrels eating garbage, inhaling bird feed, greedily demolishing pumpkins. Squirrels boldly scampering into the road. And a lot more calls about squirrel roadkill.
Read the rest of the article here, at the Washington Post online. Photo by Richard A. Lipski, of that same publication.
Some botanists believe the incredibly wet spring experienced by the Mid-Atlantic region and New England could be to blame--all that rain may have washed away enough oak pollen to have impacted acorn production. But no conclusions have been reached, and further study will be done to ascertain both the cause and effects of the dearth of acorns.