CHickens dont sweat. They lose heat through their combs and wattles. If it's really hot, and they can't lose enough heat through the combs and wattles, they pant. They are coarrying around feather duvets, and they often have to lift their wings up to try and let some air flow in.
Most of the chicks have no combs or wattles yet, so the ONLY way they can lose heat is panting. Sometimes, this isn't enough... you may remember that we lost one to heatsroke last week. Our chooks have a gazebo, a tree, and some other shade. They have an electric fan. WeThey have waterers which are re-filled twice a day (so the replacement water is cooler).
Recently we added two shallow troughs (one was a cat litter tray we bought to use as a chick dust bath, the other was a washing up bowl which is usually used when the allotmenteers need a bath). A small amount of water, we tried getting them to stand in them initially, but that didn't work. Now we use them as additional drinkers, with water refreshed seveeral times a day. We throw in some sunflower seeds (which the chicks love, but which are far too fattening for them), so the chicks have to dunk their faces to get to them.
Yesterday it hit 35 degrees and the chicks were struggling. Small Person and I ended up giving each chick a quick bath, just enough to get them damp. In the aftermath of the bath, none of the chicks were panting, and they all looked quit ecomfortable. Of course it wore off, so we ended updoing it several times a day.
I tried using a sprinkler on mist (as recommended by FlytesoFancy), but the chicks were too afraid of it.
Today, I've put bottles of frozen water in the troughs, to try and keep the water cooler for longer. Of course the chicks didn't like this change... but sunflower seeds in the water meant it wasn't long before they were trying to stand on the bottles to reach in to the water.
We've got a small area of shrub which they don't currently have access to, and I've been busy pruning the bay tree so we can get some netting round it. Then they can have that, and hopefully that will be enough for them to withstand today's temperatures without repeated bathing. I've done them once today so far.
We tried feeding the chicks some tiny cubes of cucumber, but they didn't want to know. Small Person sat for ages in with the Big Girls feeding them cucumber.