Swans moult each summer. When moulting they are unable to fly for about 6 weeks while their new feathers grow back. By moulting, a swan will replace all 25,000 of their feathers. Collectively, their Feathers are called Plumage. Breeding pairs do not moult at the same time as he cob and pen - and their cygnets - would be too vulnerable to predators. When they moult, blood still flows to their new quills for about 2 weeks, so if a quill is broken or damaged, you might see a lot of blood on its wing, which should stop after about 4 hours. If you see blood on a swan's wing, please contact us, as it may be injured and we would prefer to check it out rather than leave it.