I agree with
@Eggcessive this is a common area on the head that hens can suffer from rooster.
I have witnessed it first hand 2 times, from the same rooster. I foolishly let him have a second chance and he ended up injuring my hen again. Lesson learned the hard way by me, now I share so others may learn and not make the same mistake I did. (see photos below of the damage the rooster did the first time, the second looked similar and yes a day or two later the surrounding tissue was swollen and green. Thankfully this hen healed very well and thrived. The rooster was culled).
I'm sorry that you are facing a struggle it must be upsetting to you. A very good idea to have cameras installed. They come in handy to see what happened. The second attack on my hen I saw it on video, disturbing and heartbreaking as it was, there was no question about what happened.
I realize your situation is different and you have reason for concern, but it would also be a good idea to consider investigating a bit more, keep a cool head and don't jump to conclusions - watch your rooster and how the hens act toward him. While my hens did interact with him, they were "cautious" - hindsight is 20/20. Go back and look at the photos of your injured hen - she has scabs on her comb similar to what mine had - scabs from a rooster grabbing her. Skin is ripped...literally on video I saw my rooster grab this hen by the back of the neck and throw her.
My Krissy.
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