Last I heard, flying squirrels are one of the protected species in the U.S.
Lots of red squirrels in our creekbottom, though a neighbor up the street, the idiot who planted a yard full of pecan trees, has been trapping and shooting them so the numbers are somewhat diminished. Seems they're stealing his nuts. Duh. He's not running a business, so what does it matter? His neighborhors keep stealing his traps and he keeps buying more.
Squirrels are quite entertaining when they're in the yard, but they're noisy running around in the attic. I blocked them out with hardware cloth, a very stiff wire fencing kind of material that is a half-inch square mesh. I spent a day in the attic putting chunks of this over the air vents. I also had to patch a few holes in the soffit, and put this screen over the holes on the outside. It doesn't look great up close, but most people aren't walking around the house looking up at the soffit.
I have only one birdfeeder up now, and I today I emptied it because after the last rain the seed got wet and was beginning to grow. Yuck. The last batch of seed I bought had too much fine cornmeal it in, and even the little birds don't like it. I throw other stuff in the area near the feeder, dry bread, crackers, a variety of foods that if tossed in the compost they'd go in for anyway. Might as well make it easier on them.
I try to grow things that have seeds over the winter. Even something as commonplace as a zinnia is good for little birds--I've seen the little guys get in there and tear a dry flower head completely apart to eat the seeds.