If this belief is true, then I should have a bunch of dead squirrels in my backyard. In addition to seeking what is considered good nutrition for squirrels, I am also an avid observer of squirrel behavior.
This past summer, I took on the monumental task of tearing down an old garage that was supposed to have come down 12 years ago when I built my new garage. The project took most of the Summer. In August I decided to build a garden shed on the site of the old garage. So, this Fall, I have been racing the clock and calendar to get it under roof.
Early in October I was mixing and pouring cement for the floor of the shed. During the month of October is when squirrels start to gorge themselves with food to gain a layer of insulating fat in preparation for the coming winter. Unfortunately, my shed is located between two huge Oak trees that are loaded with acorns. The squirrels were not happy with me because my presence and efforts were disrupting their efforts to gather the acorns they were cutting. Their efforts got so vigorous that I had to erect a tent over my cement work to keep it from being studded with green cut acorns.
One interesting thing I observed as I endured the raining down of acorns on my tent was the fact that a large number of these green acorns were half eaten! It was then that a light bulb came on in my head, and I said to myself, "Wait a minute! I thought all these years that green acorns were supposed to be poisonous to squirrels!?" How come these squirrels are eating large numbers of them?
As I pondered this question, I started watching and observing the behavior of the squirrels in my backyard. Something had changed. All the squirrels that had led a quiet, symbiotic relationship with each other through the Summer, were suddenly squabbling and chasing each other and exhibiting very territorial behavior, a very hyperactive behavior. Then, I started putting two and two together.
Acorns are loaded with tannin, a substance that is like Meth Amphetamine to squirrels, and is where the term "Squirrly" came from. If squirrels are gorging on green acorns in their effort to gain weight, the tannin is going to give them a lot of extra energy, which in a sense is good because it will help them get the job of scatter hoarding all those acorns completed. The drawback is that they get short tempered with each other because the tannin also brings out the worst in their behavior with each other, which is normally very family oriented and communal.
So, the truth about green acorns being poisonous to squirrels is false. But, I would not recommend feeding green acorns to your captive squirrels unless you are in to getting your lips ripped off at the slightest provocation!