I also think they're drinking more (when they have food in their crop, or not). Just go out in the evening when it's cool, and again first thing in the morning and check their crops then. They should be back to normal.
If the birds are more lethargic than heat causes or if their throast/crops start to smell bad, they then have sour crop.
In the summer, if you want, you can use 1 ounce of organic apple cider vinegar in the water as an electrolyte. It'll also be great for their guts and crops and make sour crop less likely. Maybe if they're drinking a lot, like they are, I'd say 1/2 ounce to a gallon.
Organic is not for the philosophy of organics, but because organic is made bacterially, not chemically, and still contains the nutrients and bacteria that result that process. (That's the gunk in the bottom, the "mother" of the vinegar - the best part - shake gently before pouring out your dose to make sure you get some of that in their waterer.)
Edit: By the way, adding ACV like that won't overdose them with minerals like using a prepared electrolyte can sometimes in the summer when they drink alot. If you use prepared electrolyte, use at one fourth of the dosage.
