Metamorphoses Book 11: Aesacus
Aesacus was a descendant of Laomedon and Priam born to a water nymph. He loved the country and a nymph named Hesperie stole his heart. One day as he chased her through the woods, she was bitten by a snake and died. His sorrow and guilt made Aesacus throw himself from a cliff, but on the way down, Thetis changed him to a bird. Angry that he'd been cheated out of death, he ducked his bird body beneath the water, but he still didn't die. He became a diving bird.