Presumably you mean If I Was a Blackbird?

IF I WAS A BLACKBIRD

("Dublin street singers about 1920; and afterwards from J.M. Kerrigan")

I am a young maiden and my story is sad
For once I was courted by a brave sailor lad.
He courted me strongly by night and by day,
But now my dear sailor is gone far away.

Chorus:

If I was a blackbird, I'd whistle and sing
And I'd follow the ship that my true love sails in,
And on the top riggings I'd there build my nest,
And I'd pillow my head on his lily white breast.

He promised to take me to Donnybrook fair
To buy me red ribbons to bind up my hair.
And when he'd return from the ocean so wide,
He'd take me and make me his own loving bride.

His parents they slight me and will not agree
That I and my sailor boy married should be.
But when he comes home I will greet him with joy
And I'll take to my bosom my dear sailor boy.

Text as printed in Colm O Lochlainn's Irish Street Ballads, 1939.  The tune given is very close to that already in the DT:  IF I WAS A BLACKBIRD.