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Deep all day shade is best, with good air flow.
Misters are great, if you're in an arid climate.
Lots of cool water, expect runnier poops as the fluids go right thru them to shed heat.
I put down large shallow pans(washing machine pans) of ice cubes in the late afternoon, they'll walk in them lay down in them, and sip the water as the ice melts.
I also put a box fan in the east windows of coop, which is shaded most the day, to help cool the coop down in late afternoon.
If we are going to have a long run of very hot days, I will put out a dose of chicksaver electrolytes. Just a half gallons worth, so everyone gets some, every 2-3 days. Had to use that stuff on a heat stroked hen one summer, with a soaked Qtip on the side if her beak, so gave some to the rest of the birds too....it really seemed to help.