Blood feathers are feathers that are growing back so they have blood pumping into the feather's stem. You can see the blood very obviously at the feather's base and going up an inch or so. When one of these breaks — usually from the chicken smacking it into something, say, when flying off a perch — it bleeds and bleeds and bleeds. When a chicken gets blood on her, the other chickens can peck at it and make things much worse so you want to stop it. Here are some tips we learned from our vet, a bird specialist.
Put a blood coagulant powder on/in the broken feather tip. Even cornstarch will work; it's a thickener, after all. Then keep pressure on it by pressing your thumb down on the tip, similar to how you'd apply pressure to a regular wound. You may need to keep the pressure on for 15 or even 20 minutes. Keep the pressure on and lift your thumb up to check and if it's still bleeding, put on a little more powder and press your thumb back down on the tip. Keep doing this till it stops, holding down for longer and longer periods of time as necessary.
But what do you do if you can't hold down pressure on the feather tip for that long, for instance if there's another emergency or more than one injured animal? Put the bleeding chicken(s) in a dark, quiet room — not one with a washing machine banging in the next room. In the dark quiet, the chicken can't see and will calm down and basically go to sleep. Her blood pressure will drop, causing the bleeding to slow and coagulate faster.
The photo below shows blood feathers. The darkness where the stem meets the skin is blood. Then at the top of the stem, you can see nascent feathers poking out. It's a cool process. In the middle of the image is a broken blood feather.
