I would venture to suggest that birdsong is used as a title to provide a commentary on events in the book. Despite the appalling carnage and suffering of war, the world keeps on turning; the environment, though blackened and scarred by the horrors of human conflict, still lives on. Contrary to what the soldiers in the trenches believe, the rugged persistence of nature is not a sign that everything will turn out just fine. Birds, like all animals, remain utterly indifferent to the tragic human drama playing out beneath them.

Perhaps this is one reason why Stephen is so afraid of birds. He senses the raw animality beneath their pretty plumage and the golden tones of their song. At the front line, he must overcome his fear to help Michael when he breaks his arm. The natural world remains red in tooth and claw; amidst the mechanized slaughter of war, a brief affirmation of Stephen and Michael's homosociality provides a warm human contrast to the mute amorality of nature.

The nature that birds and birdsong represent frequently stands as a challenge to Stephen's masculinity. The traditional conception of a soldier as hypermasculine is fundamentally undermined by his homosocial relationship with Michael. At the time, the prevailing prejudice was that any degree of closeness between men beyond mere friendship was unnatural. Even if we no longer share those prejudices, we can still acknowledge that the closeness of Stephen and Michael transcends the brute immediacy of their immediate environment.

Long before the war, Stephen was embarrassed and frightened by an incident involving a flapping pigeon as he sat on a bench with his lover, Isabelle. On this occasion, an intensely human relationship was not able to withstand a sudden, unwelcome intrusion by the forces of nature. Stephen's reaction is one of avoiding nature, rather than confronting and overcoming it as he does with Michael in the trenches. Stephen can avoid nature; he can also (briefly) transcend it; however, what he cannot do is live with it. He cannot hear the birdsong and cannot appreciate the disinterested perspective on the human world it provides. In the meantime, the birds keep on singing and flapping their wings; mother nature in all her serene majesty continues to register her utter indifference to the twists and turns of human fate.