Broody hens during summer

[KCNC06]

I know this is probably a dumb question, but I've been curious and thought someone might be able to solve the mystery for me.

How do broody hens (ducks/chickens... whatever) cool their eggs when it's ridiculously hot and humid outside? Or aren't they really able to cool them and it causes lower hatch rates? I have a few broody ducks and chickens lately and wondered if I should just raid their nests and try to do daily nest hunts to try to prevent them from starting new nests. It's been abnormally hot here in central NC, daytime temps have been in the mid to upper 90's every day for a few weeks and nighttime lows rarely get below 80°. I'm fairly certain our humidity levels outside have been 90+ lately too. It's like stepping into a hot sauna and getting smacked with a wet washcloth out there.
Anyway. I feel like this is probably a silly question because obviously plenty of birds lay and hatch eggs throughout the summer. I have a bag of potting soil I can't use currently because a wren decided the open bag of soil, sitting in my garden cart, was the perfect place to build a nest and lay a bunch of eggs. But the mama wren seems to spend a lot more time away from her nest than my ducks do.
One Rouen hen moves her nest every time I decide to take the eggs. She had a nest in a broken pallet crate and then moved them about 40' to a low spot under our back deck. I have no idea how she moved them that far but the eggs from the pallet crate are gone and she's sitting on eggs under the deck. I'm assuming they're the same eggs but I guess I could be wrong. There's no sign of broken eggs at her old nest though.

 

[sylviethecochin]

Or aren't they really able to cool them and it causes lower hatch rates?

Pretty much. A chicken can serve as some insulation against the heat, but she can't really cool them off.

In hot summers (below 102℉) a chicken can actually usually hatch more eggs because the eggs never cool off when she leaves them to eat.

 

[sylviethecochin]

One Rouen hen moves her nest every time I decide to take the eggs. She had a nest in a broken pallet crate and then moved them about 40' to a low spot under our back deck. I have no idea how she moved them that far but the eggs from the pallet crate are gone and she's sitting on eggs under the deck. I'm assuming they're the same eggs but I guess I could be wrong. There's no sign of broken eggs at her old nest though.

I had a duck decide she didn't like that my poor Production Red is nesting beside her, so last week, she somehow moved some four pounds of hay and most of her eggs ten feet into the other corner of the pen. I've seen a duck get off her nest, walk fifteen or so feet, and begin walking backwards, rolling an egg with her bill until she reaches the nest.

 

[Miss Lydia]

I’ve seen my Muscovys standing up over their eggs to cool them. It’s pretty neat the instincts these birds have.

 

[KCNC06]

With the constantly high temps and humidity, I started thinking it might not matter if eggs are under a broody hens... it's like a giant incubator outside! Now that would be something crazy to see. Random eggs developing just laying off under leaf litter.