In the dark of night 2 flocks of chickens become 1. In order to introduce my new chicks (now 4 months and fully grown) into the main flock I moved them from their stall into the main coop in complete darkness. If they wake up and they (the new chickens) are already there this will allow the chickens to confusedly think the "impostors" were there all along. Chickens are sedate and somewhat stupid at night so this works. Otherwise they would probably kill the new ones. Felt a bit like Fantastic Mr. Fox as I snatched them up one by one to move them. Or perhaps Seal Team 6 (think stealth mode) as I worked by the light of my cell phone in complete darkness. In and out in 10 minutes tops, moving 11 chickens. The (almost?) full moon helped only a bit.
The morning ought to be interesting and loud in the coop because while they are more accepting of new blood they still know that something is slightly off.