here are a few other potential additions to garden soil that nature might provide for you that i didn't mention in my previous post.
pigeons can do some seed and bug harvesting and then would bring it back and let it fall around their platform/coop/roost. we have had a lot of mourning doves here that wander around and harvest weed seeds and then provide fertilizer i just don't have a single roosting place for them so they distribute their contributions in various spots around the gardens. the killdeer also can forage the surrounding areas and bring nutrients back.
peas and beans planted in rotation. field peas used as a cover crop. buckwheat.
any food wastes buried deeply enough. i try to not put anything in the trash for the landfill that can be eventually used by the gardens. we don't really get many bones or carcasses of chickens or other animals here, but when we do i will bury them in a garden before throwing them away. if it is just a bone or two i'll put them in the worm buckets and let the worms clean them up and then eventually the contents of the worm buckets do end up in the gardens and those bones too will be out there. it may take several years before the bones get degraded enough by a soil community to crumble completley but i'm not in any sort of rush. in the past there were such things as bone grinders which could speed this up, but we don't have anything like that or even a garbage disposal grinder in the sink. i suppose if i had one outside in a big sink that would work, but i'm not about to get another gadet like that when nature will figure it out in it's own time. i do know that Mom doesn't like to see bones around in the gardens so if they are poking out of the ground i'll rebury them. funny enough i've never had a raccoon or other creature bother them. once the worms clean up a bone there's nothing left that the raccoons care about.