Cold chick

You have a case of "NEW COMERS NOT WELCOMED HERE" You are not alone. It is a VERY COMMON, situation when ever adding new chickens to your existing flock. He will become part of the flock eventually. Right now he is small, and at the very BOTTOM of the pecking order. You may need to keep him isolated if being pecked on badly. If pecking not severe, then let things shake out on their own.
WISHING YOU BEST. and
You may want to search out threads that address just what you are experiencing. In the search bar on top write. "adding new chickens to existing flock" many threads will show up.

 

How old is the cockerel?

 

Good question.....he sounds really young, lookin' for mama.

@vikingbulldog Welcome to BYC!
More info on the age of all your birds, your coop and run, and how you introduced the new boy would help us help you.

Also, might want to read up on integration.....
BYC advanced search>titles only>integration
This is good place to start reading, tho some info is outdated IMO:
https://www.backyardchickens.com/a/adding-to-your-flock