Will it be fairly obvious if they are not getting enough Grit? I bought 3 10 week old Wyandottes that were kept caged up, no idea what they were being fed, but I have them free ranging and also chick crumb on 5m x 5m of rough grass with some sand, and the walls are granite so plenty of natural grit, but I never see them obviously picking it up.  They eat a lot of greenery, (I worry - too much) but they love it so I am guessing what comes naturally must be good for them?  But back to the original point, how would I know that they are getting enough?