no worries.
You will occasionally see these on him (head and other parts of the body) his whole life as he molts out old feathers and grows in new. During molts, he will get a bunch at once, which is uncomfortable and may make him a bit crabby for a week or 2 until the casings come off. Frequent baths help pin feather casings soften and open easier.
The rest of his life, off and on!
A pin feather at any given location is only there for a few days, maybe up to a week before the sheath comes off. He will continue to get pin feathers in various locations all his life. Some times of year will be worse, namely after his annual molt where he looses a lot of feathers in a short period of time and just as rapidly replaces them. Kiwi often looks like a little cactus for a few weeks after molting because he has so many pins and has the attitude of a cactus too
