I went out the back door this morning half-awake and was surprised by 8 to 10 squirrels on the porch pergolas, all collecting and grunting. My presence disturbed them somewhat but I witnessed a couple of them mounting so I figured out what was going on rather quickly. The following hour or so the squirrels near and distant were grunting, chasing, just moving constantly while randomly collecting in areas.
I think the "play" is part of the mating ritual where they show off to each other by being super active and then eventually a boy gets a hump in. The play, the mock fighting, mock mating, all lead up to this moment.
This is probably not a great time to be looking for Nibbler.