The first year is the hardest on them. After that I just worry about them when it first starts hitting the 90's. Panting is fine, that's like us sweating.
But I always have pans of water for them under the water tree (shade Tree). I water down the entire area under that tree for the ducks and chickens. I keep the ducks little pool topped up each day, for the Ducks to cool off in and the chickens also drink from it. YUCK..
If you find a hen glassy eyed, (heat exhaustion) dip her feet in a pan of water. She'll stand in it while you go get some ice cubes to cool the water fast.
Its really dangerous though when it doesn't cool down at night and they don't get a chance to really cool off. That's when I get out the ice, when it doesn't go below 87 or so at night. I make sure they get ice in the water pans during the hottest part of the next day(s). I've been known to bum ice from neighbors for my hens.
Also, don't let them get over weight. Its harder on them if they are full of fat. That means go light on the frozen peas and corn, that is what we use to fatten them up before processing. Watermelon and Cucumbers are cooling though and frozen fruit.
I don't put ice in their drinkers, but I do change their water during the hottest part of the day. They will drink more if water is fresh. I also use ACV in it, they just seem to drink more when I use it.