I have had the pleasure of raising Black Copper Marans, and Blue Copper Marans since 2007. Both lines have been very strong and healthy birds. My marans love to forage along the edge of my ponds where they feed on grass, water bugs, crawfish, minnows or anything that wiggles. They will often wade out in water to the top of their legs when on the hunt. My other breeds won't go in the water like the Marans do. They are very fond of swampy or marshy environments.
Anytime there is Hawks, Eagles, or ground predators in the area, they'll sense it and go in the barns. I have had so many other breeds I can't name them all, but none have been as hardy as my Marans.
I have had 90 to 95 % hatch rates on my French Black Copper Marans with a 6:1 ratio, 6 hens per rooster.
The hens do fairly good laying in winter months here in south Louisiana, however in hard freezing cold I sometimes see a slack in eggs. but never had them completely stop laying. I find Marans produce close to the amount of eggs as my Buff Orpingtons, but the rich taste of the dark eggs is worth the difference.