gullets as attritor mills

I have read that ducks love to pick spent birdshot off the bottom of their habitat, and the incessant rubbing of stones against the shot in their gullet gives these ducks lead poisoning.

Mollison's Design Manual doesn't mention this mineral milling action as one of the outputs of a chicken, but I wonder if it could be useful.  Particularly, I wonder if mixing appropriately-sized charcoal pieces into a bird's grit would be worthwhile, and what effect it might have on the bird.  I also imagine supplying grit of two different hardnesses, the softer one containing trace minerals needed by the bird and/or the soil, might be a less-laborious method of producing rock flour.

Any thoughts?

I think however the minerals are provided to the animals they will end up one way or the other back into the soil, especially if you bury the eventual carcass. I wonder if chickens would be choosy if you offered them a variety of grit?

Joel Hollingsworth wrote:Particularly, I wonder if mixing appropriately-sized charcoal pieces into a bird's grit would be worthwhile, and what effect it might have on the bird.

I don't think charcoal is poisonous (supposed to be good for absorbing toxins....) so doing this might produce ready innoculated biochar! Distributed by your little garden helpers

I wonder how long biochar would last, in a bird's crop, with the grinding action that would take place. It does not take much force to break up biochar in my experience. The rate of consumption might be higher than with just grit alone so I'd be tempted to offer the char on its own, similar to how the grit is offered.

I tend to drop big pieces of charred wood in my chicken run for them to peck at as I obtain it.