I found Maine version in the Middlebury College Helen Hartness Flanders collection Hanford Hayes

just the chorus, but a nice tune. I've been transcribing Maine stuff from there.
We (Castlebay) just recorded this adding other lyrics on our new album of sea songs from Maine "Bound Away" (shameless plug)

IF I WERE A BLACKBIRD
Helen Hartness Flanders Collection
Sung by Hanford Hayes   Stacyville Maine May 1942

If I were a blackbird,
I'd whistle and sing
I'd fly to the vessel my true love sails in
I'd light on the topmast and there build my nest
And sing a sweet song to the one I love best