What’s causing this?

[Jayteetee]

Our 2 month old bantam Australorp has a feather issue- they look like they’ve been nibbled at?
What’s causing this? Is this a rat eating her feathers? Is it another chicken?

 

[nuthatched]

Looking at the lines on the feathers, those lines may be indication of weaknesses and they're snapping off.
It could be genetic or nutritional.