Hydration is key with my flock. Giving electrolytes in the water helps. When they are drinking more and eating less they can get out of balance.
I also give mine watermelon.... Not to much mind you. They will tend to load up on it and have reduced protein intake because of that. I give half of a large watermelon for my 32 chickens twice a week during heat waves.
I add electrolytes to two out of every three water dishes. They have the option then to not consume it.
I get home from work, let the dogs out, set the hose to run in the run and get the third dog out. By the time the dogs are done with business the water has made a nice cool pool in the run. Most of my birds are standing in it and a couple actually lay in it.
We get over 100* here for days on end.