In Tennyson's The Marriage of Geraint, the protagonist, Geraint, has just heard the song of Enid, the daughter of his host, Yniol. When Enid's song concludes, Yniol says the following to Geraint:
'Hark, by the bird's song ye may learn the nest,'
Said Yniol; 'enter quickly.' Entering then,...
What is meant by the expression, "by the bird's song ye may learn the nest"? Is the nest referring to Enid? This would be supported by the fact that Tennyson has just compared Enid to a bird. And yet, the phrase would be a strange way to describe her; one would rather say, "By the bird's song you may learn its beauty/form," not its nest/home.
On the other hand, if the phrase is supposed to describe the poor condition of Yniol's and Enid's home, then it seems strange that the subjunctive is used ("ye may learn"), rather than the indicative (e.g., "you will find [the condition of]").
In sum, what does Tennyson mean by this phrase?