The songbird represents Siddhartha’s inner voice, which he vowed to listen to as he explored the sensual side of himself. In the beginning of the fifth chapter (“Kamala”) Siddhartha told himself, “He wanted to strive for nothing but what the voice commanded him to strive for” (19).
Slowly through his time spent learning the sensual and physical side of himself with Kamala and Kamaswami, Siddhartha’s inner voice gradually becomes quiet. He indulges his senses through food and drink, gambling and Kamala. “Siddhartha's new life after he separated from Govinda had become old, losing color and splendor as the years went by, or gathering wrinkles and stains, and showing ugliness here or there. Hidden at the bottom, disappointment and disgust were waiting; Siddhartha did not notice it” (31). Siddhartha only noticed that his life had become stale and miserable. He had reached such a point of self-loathing that he had giving himself to the idea of suicide. Siddhartha felt that the bird, which was a symbol of his inner voice, had died. “Dead was the bird in his heart” (34).
He went to the river to throw himself in and end his life when he heard the holy word, “om,” which reminded him of the indestructibility of life and wheel of reincarnation. He has a wonderful epiphany and realizes that his inner voice has not died. “He laughed because the bird, that joyful source and the voice within him was still alive after all” (38).
So in that sense, the songbird (and Siddhartha’s dream that it had died) symbolized the effects of the “essential” (physical/sensual) world on Siddhartha’s inner voice.