My chicks are dying for no apparent reason

[yoker]

I have several chicks ages 1-3 months they were healthy untill just a few weeks ago when 2 of my Buff Orpingtons started moping around not eating or drinking. Then today my Isa Brown Roo who is usually the top of the pecking order got trampled a little so I picked him up and gave him his own pen and he seemed OK untill this evening. Now he bearly moves?
What is Wrong.

 

[yoker]

Update:
The Isa brown roo had a seizer and died.
But my other roo like him that was acting like him is fine now.