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Immature feathers, called pin or blood feathers, grow out of the skin rolled up in a tube-like structure called a keratin sheath. Normally, the bird will use its beak to "preen," or rub off the keratin sheath, which will allow the feather to open up. These immature feathers have a large blood vessel in their center and if the pin feather is torn or damaged, it will bleed excessively. The entire feather in its sheath must be pulled firmly from its attachment to the skin and pressure applied for a few minutes until the bleeding stops.