I have a 3 week old silkie/Americana mix chic and noticed these really thick shafts/spikes on the back of his/her neck... does it look like normal feathers coming in!? No other chicks have it.
Those are just new feathers coming in. They probably look thick to you as they will come in with a waxy coating on them. The coating will fall off as the feather gets bigger.
Nothing to worry about. Completely normal and healthy!