When do chick(en)s start to sing?

[-Olive-]

My seven week old chicks have been trying to cluck cluck for a few weeks now but a couple of times I actually heard a full on song like the egg song bbbbbbuckark bbbbbbbuckark bbbbbbuckark! I wonder what it means at this age? Maybe they are telling the younger chicks off?

 

[Sussex19]

Mine usually start to sound grown up around 10 week? Something like that.
At that age, it tends to be when they are complaining about something, or occasionally as an alarm call. (In adults, the egg song sounds similar to the alarm call)