I know this is super old...bt it bugs me i can't fig this out...my now 1.5yr old hen out of 5 is only 1 w/ this "neurological" type bobble of the head that ONLY lasts 3-5secs & ONLY when she gets a little scared or nervous ORRR when she scratches & her head moves really fast from the scratch...
I'm learning: it's not that the hens wing feathers come in faster, its that they have longer wings usually multi layered reaching closer to the tail as to cup babies etc where as the roos have very short tucked to the body single layer wings ;)
Wow I'm seeing this was 2017...what did you ever find out abt fern???? I have 1 obvious roo and 2 that have nvr made A PEEEEP....they're 8mos or so...you can also tell by feeling on the inside of the legs for the ugly rooster claw or little bump that it's starting to form!!!