The Hamsa is an aquatic bird in Hindu mythology and is often used in Indian and Southeast Asian decorations. The Hamsa is said to be a symbol of perfect union, balance, and life, and, if you constantly repeat its name, it changes to 'Soaham' which means 'That I Am'; thus it is identified with the Supreme Spirit, or Brahman.
"The sacred white goose that Brahma rides in Hindu lore. The sight of pure white flying the winter skies symbolizes the efforts of the Brahmins trying to obtain Brahma's knowledge. It is said that is why Hamsa became Brahma's steed."
—Shin Megami Tensei: Strange Journey Compendium
Devil Survivor 2
"A holy white goose which serves as the steed of the Hindu god Brahma. During winter, geese migrate over India. These majestic white figures flying through the sky became symbolic of Brahmin dignity as they tried to reach Brahma, the god of knowledge. This may be how Hamsa came to be seen as Brahma`s steed."