Thanks all. Came home tonight from Zoo Creatures and discovered another one on its back. I went to take it out and realized its heart was still beating (thanks to their translucent skin I could see it), so I righted it and put it back. Its probably dead by now, as I have not checked on it in a few hours.
I don't have a clue as to what is going on. This one looked better than the last one. Do these creatures all of a sudden become terratorial and kill each other? (I forgot to mention, that each time I find one its outside the hide. When I found the first one dead, there was a live one right next to him. It almost seemed as they were chased out of the hide, but that could be just my imagination.)