Tortoise, dead or alive?

My daughter and son in law were "given" 2 male tortoises. They are about the size of a saucer, as in cup and saucer. They live in a large aquarian (sp?) w/ bark dust 3-4" deep and a bowl of water and food. Daughter and son in law are out of town and we are tending to the critters. They have been with us since Sat pm. It is now Monday noon. On other times we have had them the food was almost gone and the water really needed replacing every AM However, since Sunday one of the fellas has been buried under the bark chips and the other one fixed in one corner. He has just started to move toward food in last 10 min. but slowly. Do you suspect the one buried is dead? I just don't want to go poking in there.