Primarily birds.
The males eat the same kind of food as the females–don’t they? But eggshells contain calcium carbonate (CaCO3) and, since the males don’t lay eggs, do they just have heavier skeletons? Or do they excrete the excess? In other words, where does the CaCO3 in the food of the males, who don’t lay eggs, go?
It’s excreted.
There is a lot more calcium in the skeleton of a newborn mammal than there is in the shell of a newly laid egg. Added to that, female mammals need to continue excreting large amounts of calcium in the form of milk for an extended period after the young are born, so the relative amount of calcium loss from female mammals is far higher than for birds
It’s possible that female birds eat more things with calcium, too - birds will chew/eat things like eggshells, shed antlers, bone, clay, etc. for the minerals, including calcium. It’s possible female birds are more driven towards those things than the males, upping their calcium intake.
They eggscrete the eggcess. Sorry.
In addition to the points already made, bear in mind that the differential calcium requirement is not huge in quantity or time apart from in the very special case of chickens which have been evolved by humans to crank out an egg on average every 1-3 days. Apart from that one case (which is obviously of enormous interest to humans) it’s a matter of a few weeks per year when the female needs a bit more than the male. Hypocalcaemia in birds can manifest as muscle weakness, spasms etc, which can show up outside the laying season and can affect males as well as females.
My mom gives her hens a handful of ground oyster shell with their feed every few days. She doesn’t have a rooster, but if she did, I presume he wouldn’t get the oyster shell.
I doubt that a rooster could be dumb enough to try to take food away from a feisty group of hens!
I’ve seen smaller breeds of roosters worry much larger hens. They flutter nearby, squawk, harass and even claw at large chickens. And any bird will instinctively back away from a dedicated assault – thin bones break easily, and a grounded bird is a dead bird. Even if a large hen can’t fly far, or even at all, instinctively, they avoid damage.
Testosterone. Its a hellava drug.
Besides calcium needs for bones, calcium is also essential for nerve excitation and muscle movements.