What turns it into a problem: it looks excessive and obsessive rather than incidental, birds losing weight or looking unwell, droppings changing a lot, or them swallowing foreign objects rather than stones. Nails, screws, wire, plastic, string. Swallowed metal and sharp things cause serious internal injuries and they are not fussy.
So walk the half acre, especially anywhere there has been fencing or building work, and pick up every bit of metal and twine you find. That is a better use of an afternoon than worrying about the soil.