There's an old animated film (80s or 90s) that me and my sisters used to watch. I think it had to do with swans or some humans turning into birds by some curse. It's not Swan Princess and it's not Wild Swans. I remember this one part (spoiler alert?) near the end where the protagonist tries to save a crystal or some other fragile object from breaking when falling to the ground, he jumps and doesn't catch it in time so the thing shatters and so he dies or turns into something else? Like that crystal held the curse or something. Pretty sure it was swans.
The ugly duckling? Idk lol