Consider removing lower tiers and replacing with something like a stand alone sawhorse.  You might also increase available roost space in upper tiers to reduce strife as setting in for night.  Get them roosting up.  I bet a mink can not make a 36" plus jump.  Could you setup a baby monitor and have a dowel to use as a weapon?
	
		
			
		
		
	
				
			
	
 BF borrowing a spring trap that hopefully his coworker remembered to bring today. I'll take the bottom roost out later; I don't think it's needed anyway now that I'm down to 15 chickens.
	
	