Been raising chickens for about 4 years but never had this issue. I had 14 baby chicks hatch about 2 1/2 months ago. I have 3 left. I usually hatch at the beginning of Spring and by the time the hot Texas Summer hits they are old enough to handle the heat. Not sure if this is the issue, they seem healthy and I have them in a large covered coop by themselves. Water is refreshed 3 to 4 times a day. I don’t understand what’s happening other than the heat. Temp in Texas is about 100 to 105 day time and around 80 at night.