Hen suddenly became agressive towards one of my other hens. But I have a rooster.

[PoppySeedy]

This literally just started this evening but I go outside to check on my hens and saw my black copper maran was/is terrified of my bluebell hen and she's been hiding on the roof of their house. Idk what happened between them but when I put the maran on the floor the bluebell went for her. What can cause sudden aggression like this between hens when I have a rooster? And what should I do?

 

[CluckerFamily]

How is the bluebell hen?
Is she showing any signs of sickness?

 

[aart]

This literally just started this evening but I go outside to check on my hens and saw my black copper maran was/is terrified of my bluebell hen and she's been hiding on the roof of their house. Idk what happened between them but when I put the maran on the floor the bluebell went for her. What can cause sudden aggression like this between hens when I have a rooster? And what should I do?

How old are these birds, in weeks or months?
How big is your coop and run?
Dimensions and pics would help immensely here.
Cock/erels are not always good at breaking up fights.

 

[PoppySeedy]

How is the bluebell hen?
Is she showing any signs of sickness?

No signs of sickness