20 weeks and my roosters are still not crowing (RIR)

[Chickie Pia]

Is it normal that none of my roosters are crowing? They were born at the end of November 2013.
Only their dad and my bantam roosters crow.

 

[familyfarm1]

Maybe they don't want to because there dad is the top rooster and their scared?

 

[Chickie Pia]

Hahaha! No he is really chilled with them. Even let's them eat his food. He has never attacked any of them.