The eggs in the culvert sound like my experiences! My bantam hens are 6 & 7 months old & I get several eggs, but not nearly enough to account for the hen population. Even though I walk my yard often, I can't find new nests. Then, I find eggs in a flower pot or on the bare ground. They have nice, comfy nest boxes in the chicken house; why do they ignore them?! I put a box of hay on my porch for a kitten to sleep in. Now I get eggs in that. I've tried big overturned pots with hay and a golf ball as bait ("ooh, look at this, wouldn't it be a great place to lay?") scattered over the yard. I'm hoping there's not a huge nest under my house, since it's up on blocks and chickens go under the house (& I swore they wouldn't do that because they wouldn't go where it's dark). When I do find a pile of eggs, I'm afraid to use them because I don't know how long they've been there! So I keep looking every day!