I had an idea with regards to growing your tribe.
What if when you are looking at places to migrate on the migration map, you could see AI camps.
There is a chance that there is another tribe in your proximity. When you do decide to migrate you can walk in an AOE near that camp with a chance some tribe’s people will join you as you pass.
Even if there was an icon above the AI tribe giving you a percentage of how likely someone would join. At least then you have an indication so you can choose if you pass close by or not.
It would change the dynamic between camps after migration due to numbers increasing on the move.