Swan may

The Swan Maiden (or Swan may) is a mythical creature who shape shifts from human form to swan form. Despite the name, males are found in a small number of legends. The key to the transformation is usually a swan skin, or a garment with swan feathers attached.

Swan may in "The Man who Came Late"
Alianora was a swan may. When she wore her swan feathered bodice, she transformed into a swan and could fly. After the great war of Order vs. Chaos, she continued to transform and fly to explore the countryside around the village she settled in. When her daughter Alianna came of age, Alianora passed the swan garment to her and Alianna became a swan may.