I have just discovered that one of my 4-week-old Rhode Island Reds has died over night. During the day my chicks are kept in a fenced-in area of about 100 square feet in the shade of a very large Pecan tree in my backyard. I move the fence every other day to give them a new spot of grass. At night, I keep them in a very large box of about 20 square feet which is inside an outdoor shed on our property. I lock the shed every night. They always have food, water, and a heat lamp shining on one corner of the box. We live in Southeast Georgia, USA, and the temperature has been in the upper 60's at night and mid 80's during the day. The dead chick was still in the box with the other chicks. There was no sign of any injury. Does anyone have any ideas about what could have happened?