Q.small holes in the ground
These holes are usually in areas with bare soil, have a small mound of earth around them, but what makes them especially mysterious is that the holes usually are intentionally blocked by pine needles or other organic debris. The one that really had me scratching my head had a leaf nicely curled into a funnel blocking the entrance to the hole. I just can’t see an earthworm managing that!
It sounds like a critter of some kind has taken up residence in your yard. This article may help determine which it could be: https://www.gardeningknowhow.com/lawn-care/lgen/lawn-and-garden-holes.htm
I'm sure it's not birds because the hole actually continues into a tunnel of exactly the same diameter as the hole and I've pulled out pine needles and little sticks that are drawn an inch or more into the tunnel. As well, nothing is tucked into the tunnel in the way of edible items but as yet I haven't excavated the areas to be absolutely sure.
I suspect it was birds – either jays or crows. They are known to dig small holes to hide food (like nuts) and cover them to hide them.