I like to imagine that Emily’s inspiration for this poem was her watching a bird build a nest within which she raised her young, but the young have all grown up and the mother leaves her nest one final time before winter comes. And as Emily watches mamma bird fly away she thinks about how sad it will be to lose not only her relationship to the scene she spent many hours watching, but how the act of flying away to start over anew is like love leaving our heart and, perhaps, leaving a shade of death inside our heart.
The first line of the first stanza says that she was not surprised that the bird stirred her “pinions” (wings) and flew away from the now useless and forgotten nest. Obviously the bird can’t spend the rest of its life there, but the second line reads as if she has to convince herself – “So I said – or thought” – because otherwise she doesn’t want to believe the bird will leave. Logically she knows the truth, but emotionally she can’t let go. Of course this is the difference between her (us) and the bird because the bird doesn’t care, only we do because we use words and language to form attachments to things in ways that animals cannot. Emily even says “This was but a story” so she acknowledges that what we do as humans is use language to construct our reality. And the bird may even have been aware that Emily had been watching her all spring and summer, may have even come to expect scraps of food from Emily’s hand, but once it’s time to leave, she leaves and is not coming back. But Emily can’t let go of the relationship because she is not a “Birdling”.
And though we know Emily is saddened by this state of affairs, the second stanza is quite hopeful and filled with life and the renewal of life. The bird will find a new forest and a nicer branch to build her next nest, and her new (“modern”) mate will be receptive to her desire to ‘be fruitful and multiply’. And Emily’s use of the word “vow” is important in that it speaks to the responsibility God put on humanity to mate and have children. Of course we humans take it further and a vow for us often refers to marriage and the taking of a mate we will not fly away from at summer’s end. Of course Emily might also be more clever (perhaps even subversive) than we realize in that she could be saying that “God’s old fashioned vows” are outdated and unnecessary since the birds can find a new mate whenever they want so why can’t we?
And if she is being subversive, then the third stanza could be saying that she wonders what if she acted like the bird and flew off to find whatever company she wanted whenever she wanted it. In modern terms we might say a person like this is a player, and so I’m not quite sure Emily means it to that extreme, but she is wondering what it would be like if that love inside her found “gayer boughs” in “broader forests”.
The final stanza, however, seems to be saying that when love leaves us it is like being dead, as if “There were just such [a] coffin / In the heart instead”. The empty nest is like a grave, the broken egg shells more now like coffins than the vehicles of new life, and the tree is like her own heart within which there are only dead and forgotten things. Perhaps she is also referring back to those “vows” that, if broken, can only lead to death since breaking God’s original vow would mean not being fruitful or multiplying. In other words, no kids, no means no more life.