Welcome to BYC, glad to know you have discovered how wonderful (grand) chickens are! You have received lots of good advice re how to keep chickens cool during summer heat. A chicken's normal body temperature is 105-107 degrees, and on top of that they are clad in a warm down coat, so keeping them comfortable during summer heat waves can be a challenge. In addition to ideas listed above, chilled summer fruit and vegetables such as watermelons, blueberries, tomatoes, squash, etc can help keep them cool and also provide good vitamins, minerals and electrolytes. I also run soaker hoses under shade trees during dry, hot summer heat, and the hens clearly enjoy standing and walking in the cool well water.