Our marginated tortoise has recently started to dig himself down a few inches (3-5) into the soil in his enclosure. Always in the same area (under one of his favorite plants...sometimes under its root ball). He's outside with daytime highs in the mid 80s and night time lows 65-72 right now. Is this normal? Should I be doing something extra for him? He never appears to eat anything we give him, but has lots of edible plants in his enclosure and pooping, so I've stopped worrying about that. He's our first tortoise so we're new and I don't want to mess up.