Bully: One on One

[Woodys Chickins]

Flock: 5 hens (2 RI Reds, 1 Delaware (white), 1 Ameraucana (Black), 1 mix Ameraucana (gray))
Age: 1yr 6mos (all)

The Delaware girl is the largest of the girls. Recently (last month), the Delaware has been bullying one of the Reds. She only bullies the specific Red; doesn't bother the others, and the others do not participate in the bullying.
Observations:
(1) The Delaware stopped laying about a month ago. I attribute this to natural seasonal slow down. The others are also slowing down--except the Reds
(2) The two Reds are my most consistent egg layers; both lay nearly every day.
(3) No obvious disease or sickness.
(4) Same feed (Kamblauck Henhouse Reserve). Same water.
(5) Good size "run" (85 sq feet); also free-range daily. Good size coop (24sq ft).
(6) When I isolate the Delaware from the others, she hates it...behaves like a wild animal pacing back and forth. (truthfully though, I have not isolated longer than maybe half-day...should I separate the Delaware longer?

Appreciate assist!

 

[FrostRanger]

More details about what's going on? Who's doing the bullying? Who's the victim? What's their diet? How big are their coop and run in square feet? Do they free range? You have some pictures of your setup?

 

[rosemarythyme]

x2 on photos of the set up.

What specific things is she doing that's bullying? When does bullying occur (like around food, only inside the coop, etc.)? How does the bullied bird behave?

 

[FrostRanger]

I would separate the Delaware for a week or 2 to reset her position in the pecking order and reintegrate her. If that fails, put some pinless peepers on the Delaware. If you don't already add some clutter to your run so a bullied bird can escape the line of sight of another and add a second or third feeder and waterer so the bully can't guard it. Pictures would still be helpful so we can give specific suggestions

 

[Woodys Chickins]

1) I believe the "set up" is irrelevant since the behavior occurs inside the 85sq ft as well as on 2+ acres of open land.
2) Behavior: The Delaware simply has to look at or see the Red, makes a low growl, then makes a bee-line run to lunge at the Red trying to attack her on the neck or head. Occasionally the Delaware will attempt to grab her and hold onto her to peck. ((Thus far the Red has avoided notable injury.)) The Delaware simply doesn't like the specific Red. The others get along and tolerate each other just fine.
Set-up: The RUN is nearly 7 ft wide x 13 ft wide x nearly 6ft high. Fully enclosed in 1/2 hardware cloth.
Feeders: 3 separate feeding stations
Water: 5 gallon bucket with 5 separate "cups"
Baths: 2 separate (2x2) dust baths ((wood ash treated with insect dust))
A couple tree stumps for them to jump onto, as well as a 2x4 roosting bar mounted 3ft off the ground.
They're allowed out of the run each morning.. they all exit excitedly. However, after the initial excitement, the victim Red will avoid integrating with the group since the Delaware will soon start growling if she approaches the group.

B/L I'm thinking to isolate the Delaware for an extended timeframe.

 

[Woodys Chickins]

Update
The atch photo is the Red victim. Today I noticed this (circled) on her lower mouth. I suspect it's either a pimple or result of a bully pecking injury.

?