Wow!. Thank you so much to everyone for all your help. What a fantastic group! I feel fortunate to have so many smart chicken lovers working to help solve this problem. I have a friend dropping off a trap today but as Art pointed out the trap may catch something other than the culprit. I saw a grey squirrel approaching the pen so that is why I thought is was the squirrel. The cracked corn and crumbles remain untouched. In the past when this are was used to house metal garden steaks and tomato hoops we had chipmunks living there. Also, a few days ago, before I realized there was a problem I had my 4 1/2 week old chicken in the pen for a day outing while I worked in the garden outside their pen so I had a direct view in. During this time (middle of the day) a new hole appeared, chicks were unharmed and made no noise to indicate trouble, and their food was untouched. I do have a camera that I plan to put up but I need to get an extender to access WIFI from the house. I think that is the best thing now to definitively identify the criminal. Aside from the detective work, I have ordered the hardware cloth which should arrive by June 4 and plan to dig down a few inches in the inside of the pen after taking everything out ( ugh!) the line the bottom with HC and attached securely to inner wall so it is sealed completely from any diggers.