Why are my hens getting this wound?

[RoosterJuice]

Hello, I am wondering why 3/19 of my hens have this wound in the same spot. There are no roosters among them. They are in a portable tractor so they have access to fresh grass every 2 days. I noticed the wounds fresh 2 days ago, they seem to be scabbing over nicely now. Does anyone have any suggestions as to why this may happen? Did they pull their feathers out out of boredom? Were they being bullied by the bigger hens? Is this because they went a few hours in the morning without food around the same time? Is it because their area flooded around that time and they were stuck in the mud and roosts until I moved them? I attached a picture, please let me know what you think.
Thank you,
-Andrew

 

[sourland]

How much space do they have? To me it looks like feather pecking/plucking due to boredom.

 

[RoosterJuice]

How much space do they have? To me it looks like feather pecking/plucking due to boredom.

Thank you for the comment. They are in a 12x12 mobile tractor, moved every 2 days. They were raised in it, maybe now that they are 5 months old it is time to move them to the big coop? I get about 6 eggs a day now. I didn’t think the area was an issue. The wounds are all above the tail on the top side of the bird. Is that the area where they would typically pull out feathers due to boredom?

 

[sourland]

I'd move them to the big coop - 'just in case'. Feather pecking/plucking especially of the pin feathers can escalate to cannibalism.