I recently added 10 new ISA Brown birds to my existing flock of seven. My one rooster and two hens act very aggressive towards them and will not allow them to roost with them at night. These birds came from a large chicken producing facility. They prefer to stick together and will not move and do not wander like my free roaming birds. How do I make the transition easier for them? What should I have done? (first time introducing new birds) Thanks!