2 day old chicken act like a rooster already ?

[Eifelhexe]

do 2 day old baby chicken roosters already behave as such ?

i have a 3 week old Serama wich is definately a boy
in the same cage with a bunch on 2 day old chickens but with a fence between them so they could only see each other.
today i took the fence out and the Serama was imediately attacked by one of the 2 day old. and that little one wont give up attacking
even though he is almost half the size.
well i think i better seperate them again
but is that a sure sign that this is a rooster ?

 

[sydney13]

it probably is

ive heard if you scare them by swishing something over their heads the girls crouch down and the roos stand up or if you pick them up by the beak the girls go limp and the boys try to get free, these are probably worth a try