Public land squirrels around here all wise up after opening weekend.
One thing you never hear anyone talk about with squirrel is playing the rut, just like deer. They do it twice a year. If you catch them right, they are incredibly active and vocal. Be mindful of the boars when cutting them up. They have scent glands scattered around their body. There's so little meat, that a little bit if the scent gland will ruin the whole squirrel. You can tell if you get a rutty boar because his scrotum can be as big as a 50 cent piece. Other times during the year, they will actually retract their testicles inside. Here in Ohio we have American Red Pines, Eastern Grays, and Fox squirrels. I've given up shooting pines because there's not enough meat, gray's taste the best and Fox's are biggest.
What I'll do is just sit near a heavy mast tree or den tree for about 15 minutes. Once the birds start chirping I'll make a call with my mouth from the very back of my cheek by sucking in. This usually will get a bark back about 45 seconds later. This lets me know which direction to start scanning tree tops with my binoculars looking for a limb swaying from the weight of a moving squirrel or the flicker of the top of a tail. Shotguns are very effective this time of year as they are moving around a lot, but I find they ruin too much meat, so I stick to 22lr for head shots.
On a good day, I may see eight to ten in the tree tops, but may only be able to get a shot off on 2 or so. If I can get a shot off, I'm probably taking him home 75% of the time