

And it is said that Elwing learned the tongues of birds, who herself had once worn their shape; and they taught her the craft of flight, and her wings were of white and silver-grey. And at times, when Eärendil returning drew near again to Arda, she would fly to meet him, even as she had flown long ago, when she was rescued from the sea.
“Of the Voyage of Eärendil and the War of Wrath” - The Silmarillion - J.R.R. Tolkien