CCUK
Free Flying
The weather in my fair Isle had been very British! Meaning mostly rain and cool. Today however it is 34c on the loft. I have put a bath in for them and they loved it! The youngsters won't use it but like @backyard pigeons says, a fan blowing cool air through will help. So long as there is cool water for them to drink they should be fine.
Should I be overly concerned about panting squabs? The loft has plenty if not too much ventilation and there's only one point for about 10 minutes in the evening where the sun can shine directly towards them, its just plain hot!
The other day when I first noticed them doing it I took them inside to cool off. Fortunately the parents are very lenient about me messing with their young but I cannot reasonably move them inside permanently to keep them cool.