The odd thing about it is that up until this weekend, there was no hole there. I've mowed that spot all summer and I have to watch very carefully there because it's right at the cusp of the hill that drops down toward the pond. I also have to watch for the turtles that like to lay eggs in my mulch and the babies that hatch from the eggs. Is it possible that they moved from another nest or started a new one this late in the summer?