I think If I Were A Blackbird is an Irish song; Delia Murphy recorded it, and I *think* it's in Dublin Street Ballads collected by Colm O Lochlainn.

My favourite verse:

"His parents do spite me, nor will they agree That I and my sailor boy married should be But let them deride me, and do what they will While there's breath in my body, it's him I love still"