4 of 7 chickens losing feathers below vent

[Nrelax11]

So about a week ago I noticed two of my chickens were completely bare below the vent. I got concerned when it looked a little red and swollen, but I thought maybe that's just how it is below the feathers. Then a couple more birds started losing their feathers back there too. One of the Australorps is starting to lose feathers down her leg. Anyone have any ideas of what it might be? I did realize that their chicken run is right under a big tree where birds hang out. They were pooping a lot on the chicken runs roof and the rain was washing it down the side. I don't know if this could be from parasites or something. Any help would be much appreciated.

 

[azygous]

You've neglected to state your location in the world. It gives us more information than you might realize that we can use to help you.

If you repost the photos and select full size, we can zoom in and see detail.

 

[Nrelax11]

You've neglected to state your location in the world. It gives us more information than you might realize that we can use to help you.

If you repost the photos and select full size, we can zoom in and see detail.

Sorry, I'm in Washington state. Near Tacoma.

 

[Nrelax11]

I should also say that one of them is started to lose her feathers along her thigh area on the back.

 

[Finnie]

I would dose them with ivermectin, wait 10 days, and dose them again.

I’ve never seen anything like this on my chickens, but my knee jerk feeling on seeing those photos is mites. I would assume those hens are feeling awfully itchy.

 

[HorseGirlAbby]

It could be them pecking each other's feathers out. During the winter months, they often get bored, and pecking other hens is a distraction. Are they grooming themselves a lot, more than usual? If so, it's most likely mites or lice.