this story has been told in a number of ways and the basic gist is pretty much always the same: a varying number of older brothers get turned into birds of some kind (usually swans, geese, ducks, or ravens) by a female family member that wants them to just go away and and so the clever and devoted little sister must search them out and break their curse. There are some variations that don't include the brothers turning into birds, like the North African story "Udea and Her Seven Brothers," but even that involves assistance from ravens and pigeons.