Silkie Roo Conundrum!

[OffBeatBetty]

So, I have been quite unlucky and I believe the 3 silkies I have are ALL roos. They are about 4 months old, and my black one started to crow a couple of weeks ago. His crowing is very mild, however (more like a gurgle/ choking noise, lol) and he usually only does it a few times a day. I have a small flock of 8, and obviously 3 roos is far too many to have. The other two silkies haven't crowed at all and I'm not sure if that's just because the black is the dominant roo... or there's an off-chance the other two might actually be pullets? Most people have told me that ALL their roosters crow, so I'm wondering why the other 2 aren't. Shouldn't they all start around the same age? They all look pretty identical: large combs, wattles, and little "streamers" in their crests... but I think it's strange they all aren't starting to crow at once. Is that normal? Or might this indicate pullets if they aren't crowing (I guess you could say I'm looking for a glimmer of hope here)
Thank you!

 

[woodsygal]

Crowing is like egg laying, they start when they are ready. Cross your fingers you get an egg instead of a crow.