Theory:

"The Legend of Northland" is a poem written by Phoebe Cary. It is a ballad that narrates a legend from the Northland.

Contrary to certain interpretations available online, the "Northland" in the poem doesn't refer to the place in New Zealand. Instead, as mentioned in the introduction, the story that the ballad narrates is set in Norway and is drawn from a Norwegian fairy tale called "Gertrude's Bird".
 
The poem talks about an incident where greed and selfishness in a human was adequately punished. The poem has three central characters. They are,
  • The speaker/narrator
  • A woman
  • Saint Peter
There are different versions of the story, but the principal theme, motif, and plot remain the same throughout the different versions. You may read a version of "Gertrude's Bird" here.
 
The following video is again a different version of the story.
 
 The Red Headed Woodpecker**