Introducing new birds

[ReelFaster]

That is a mystery why you lost so many especially all the way up to 6 months old.

Am in a similar boat, I have 3 hens 12-18 months since Feb. Picked up 2, 2 week old chicks few weeks back (tomorrow they will be 6 weeks old). Boy did they grow fast and outgrew the bin we have them in. I slapped something bigger together out of some scrap wood I had and now in the morning I keep them outside till dark I bring them back in. I am trying to hold out as long as I can till they get a bit bigger before introducing them to the big girls.

I plan on introducing them slowly as suggested by various resources. My coop is up off the ground about 32-36" sitting on 4x4's so I built a gate under it and hardware clothed it off all the way around. Built a makeshift mini coop & perch as well inside it and plan on having the two little ones live there for 2 weeks. Only the gate is between them and the big girls so they can see each other all day and I plan on putting some food down in that area so they can somewhat interact. My goal is to do this next week when they are 7 weeks old and introduce at 9 weeks full time, if I can do 10 weeks I will.

 

[Clucking_In_Michigan]

Putting them in at night might work......or not.
Make sure you are down there at first light in case of trouble.
...and have a Plan B.

How old are the chicks?
How big is your coop and run, in feet by feet?
Dimensions and pics would help immensely here.

Here's some tips about......
Integration Basics:
It's all about territory and resources(space/food/water).
Existing birds will almost always attack new ones to defend their resources.
Understanding chicken behaviors is essential to integrating new birds into your flock.

Confine new birds within sight but physically segregated from older/existing birds for several weeks, so they can see and get used to each other but not physically interact.

In adjacent runs, spread scratch grains along the dividing mesh, best if mesh is just big enough for birds to stick their head thru, so they get used to eating together. Integration Basics:

It's all about territory and resources(space/food/water).
Existing birds will almost always attack new ones to defend their resources.
Understanding chicken behaviors is essential to integrating new birds into your flock.

Confine new birds within sight but physically segregated from older/existing birds for several weeks, so they can see and get used to each other but not physically interact.

In adjacent runs, spread scratch grains along the dividing mesh, best if mesh is just big enough for birds to stick their head thru, so they get used to eating together.

The more space, the better. Birds will peck to establish dominance, the pecked bird needs space to get away. As long as there's no copious blood drawn and/or new bird is not trapped/pinned down and beaten unmercilessly, let them work it out. Every time you interfere or remove new birds, they'll have to start the pecking order thing all over again.

Multiple feed/water stations. Dominance issues are most often carried out over sustenance, more stations lessens the frequency of that issue.

Places for the new birds to hide 'out of line of sight'(but not a dead end trap) and/or up and away from any bully birds. Roosts, pallets or boards leaned up against walls or up on concrete blocks, old chairs tables, branches, logs, stumps out in the run can really help. Lots of diversion and places to 'hide' instead of bare wide open run.
Good ideas for hiding places:
https://www.backyardchickens.com/threads/a-cluttered-run.1323792/

My chicks are 9 weeks old right now. We are expecting colder nighttime temps Friday (low of 33F) so I decided to wait another week.

My coop area (roosts etc) is 7ft by 4ft by 4ft high with an external nesting box that has 4 nesting areas with all of the needed dividers. The main run is 7ft by 17ft by 7ft high. I have a couple outdoor perches as well. I am planning on adding 2 more feeders and waterers spread out so the older birds cannot keep the younger crew away, they can't guard them all!

I have attached a pic of the coop/run (this is before the hardware cloth was added to the expansion, it is now all enclosed with 1/2 inch mesh hardware cloth)

 

[aart]

Might be tight space for 2 old and 8 new birds.
Add some 'clutter' to the run.

 

[Clucking_In_Michigan]

So far, so good with the night time intro. First am and minimal pecking in the first 2 hrs. Bernerd the roo says "I'm the boss, you girls will get along "