Swan Keyring. Swans can break a humans arm with a single swipe of its wing. Swans only become aggressive when defending their nesting ground from other intruders, whether they are other swans or humans. In England, all the swans belong to the Queen, and the swan keeper's office dates from the 13th century, supported by three swanherdsmen, and their duties related to the annual Swan-Upping on the River Thames.