On Unbelievable Stories

The account they give is that Procne, Philomela and Tereus were transformed into birds: a swallow, a nightingale and a hoopoe respectively. This is what actually happened. Procne and Philomela killed Itys and looted his house. They boarded a small boat and made a swift escape. Tereus chased after them and when he failed to capture them, he killed himself. As a result of their disappearance, people said that they had turned into birds because they vanished so suddenly.