Do you have a thermometer in there? If not, get one and hang or afix well out of their reach (you can get a plastic one for next to nothing at many places). If a bird is breathing real heavy, as you describe, it is struggling and the situation is serious if not abated soon. Give electrolytes with all that panting. In a pinch Pedialtye or Gatorade will do. Can spritz on watermelon as one way to give to them.
What is the size of your coop? (width, depth, height). How many birds?
It's hot and humid today but nothing compared to what tomorrow and Thursday will be, at least here in NJ so if your birds are already struggling, you have a real problem on your hands.
There's lots of great threads about how to keep them cool.
Examples:
Fans (some add AC)
Cold water available at all times (blocks of ice in the water will keep it cold longer)
Cold fruits at intervals (e.g. frozen watermelon slices)
No heavy food in the heat of the day
Shade shade and more shade
Electrolytes when panting is not brief
JJ
