I'm amazed by our hens' abilities to eat.
I weigh 215 pounds, and eat something like 2700 calories a day, including about 150 grams of protein. So, about 22% of my calories are protein. Those are rough guesses, not measurements.
Our hens each lay one egg a day, with around 6 grams of protein. I'm going to guess that they must eat 24 grams of protein to deliver those 6 grams, and also run around the yard and make lots of feathers. 24 grams is about 1/6 of what I eat.
The hens eat grass, cornmeal, random bugs that they find, and snails. (Martha has found no snails at all in the last year in the back yard, but clears 10-20 every week from the front.) I don't think their diet is particularly higher in protein than mine. In particular, their cornmeal is almost identical. So, each hen must each 1/6 of the calories I eat.
These animals weigh 5 pounds! (Anya just weighed them.) Per pound, they eat seven times as much as I do. Since I spend at least an hour a day eating, it's no wonder that those hens spend every waking minute pecking at something.