not exactly   true .     I  1st. bought  6 laying hens .   5 were    rir's and 1  black  austrolorp  .
5  days  later  we bought  30  baby chicks  all 1 week old .  rir's  barred  rock and  austrolorps .   
I   did  find out  one thing that is   very important   ,   AS   SOON  as  weather  permits  ,  MOVE  the  chicks  OUT  of  cages  into the  run and coopos  .   I have  never  seen  CHICKS  grow  so fast  and HUGE  like  my BO's    did  ...   they  are 3.5  months  old and   they  look  like they are  5  months  old .  Plenty  of  excerise    ,   sunlight  ,   food  , water     sure helped them   grow  faster  than  any of the  others that were caged  for 3  months .  
they were  in a  6 x6  wired cage with  plenty  of  room  , plenty of ventilation .   food and water and they  were pecking each other like crazy .  I  even  separated  the black  austrolorps  from the  rir's and a barred  rocks  ,  made no  different  to any  of the breeds  ...    I  think its  by nature they  do this .  ONLY  breed that  did NOT peck each other  were  buff orpingtons .  I had  15  in a  6x6  cage and  never had a problem  with  pecking  and  now  they  are  3.5  months old and  already  loose in  one of the coops and runs with other chickens    and  NO  PROBLEMS  not what so ever .    In that  coop and  run  , I have  ONLY  1  rooster  and  there are 20  head on that side  .  WORKS  great .  
The larger  COOP &  RUN  I have   2  roosters  and   about  65 - 75  head  .   BIG  RED    is the " ALPHA "   and   he  controls  the flock  .  Now that they are  older  ,    you will still  see  pecking and  chasing  now and then between  the   flock ,  but  not  near  as  much  as  when they were younger .  Now  .,  its  like  a playful   game  kinda  thing .
I am  going to  post  a  picture of the  Buff Orpinstons  about a month or  so  ago  ,  they were  only  2 months  old ...  EVEN  bigger  now  .