3-Week olds with bald spots

[LedgeWoods]

Any ideas what could be causing some of my chicks to be losing feathers/fluff above their tails/lower back? A few even have a hint of blood on their backs. They are all starting to trade fluff for feathers - could it be the new feathers coming in and the chicks picking at the area? They all seem happy & healthy otherwise. They were fine yesterday and noticed about 8 out of the 41 had the bald spots this afternoon. (They "graduated" from their temporary box in the workshop to half of their new coop this afternoon - they are enjoying the extra room and the little roost "hang out" area

)

 

[mrbstephens]

Could be just feathering, but they shouldn't be bleeding. Do you have pictures?

 

[chicmom]

With blood being there, I think they must be pecking eachother. Maybe they were a bit crowded in their other brooder.......

 

[LedgeWoods]

All the chicks that had the bare spots yesterday are fine today. Did watch some of the chicks momentarily picking on another's back-end today, so I would guess they had outgrown their brooder and our timing was good getting them in their new coop. Thanks for the responses!