When is it safe to put chicks in with the hens

Providing a safe place for chicks to duck into where the big chickens can't follow is only half of what you need to do to make a run safe for the chicks as they're integrating.

I have a complex run with numerous partitions, and early on I could see that there were a lot of places for a chick to get boxed in or cornered or trapped with no possibility of getting back quickly and safely to their safe refuge. So I created "portals" in all of the partitions and anywhere it was possible for a chick to get trapped for that's when injuries and death occur.

I've been using this system of portals for eight years now without any casualties. I have pics of my set-up in and article I wrote on outdoor brooding linked below my post.

From how you describe your run, it may be a long distance for a chick to travel to find its way back into its safe refuge. You may need to re-engineer your run to accommodate safety for chicks. What comes to mind is a parallel channel with openings all along the way or an opening along the bottom a few inches high that chicks can scoot under.

Thanks guys! We're going to build an extension onto our roofed coop/run that has a closing hatch to allow us to separate babies or sick birds or broody hens and can otherwise be left open for even more space in the winter months when they get confined from the outdoor system. I feel much better about their safety!