Hmm and the heat hasn't even started. I noticed it too. I am needing to supply more shade. I have heard of people giving their chickens a big ice block in their water. Mine are all walking around with their mouths open. Lots of water available.
I have chicks, 25 days old. They're walking around with their mouths open too. We decreased the wattage on the bulb, but I still had to pull it back a bit today (and clean their water 3 times). Thankfully, their coop will be under an 80-year-old tree, so they'll be fine this summer.