Is this behavior concerning?

[MetalheadChickenLady]

This one speckled sussex is obsessed with pecking at the tail feathers of the leghorn chick, specifically. doesn't appear to be attempting to pluck the feathers out, doesn't grab and hold on and tug- just poking. Doesn't do it to any of the other ones. the leghorn seems unphased... for now.

 

[Mrs. K]

How much space do you have them in? How old are they? I think they may be too crowded. I would not want this behavior to get worse.