Holes by my deck

Holes under my deck

I’ve noticed that I have a few holes in the ground along the edge of my deck that are pretty recent (two picture above). They’re about 5cm to 10cm in diameter and there are five that I can see along one half on the same edge.

Any idea what might be causing these? Less worries if it’s four-footed and more so if it has more or fewer feet! Im in Adelaide, Australia where it’s been particularly cold (under 4 degrees C overnight) and wet the last couple of weeks, but don’t think this is weather or water related.

Any suggestions greatly appreciated.