Birds are belongs to the series 'the things you own end up owning you' referring alienation and freedom.
According to the simplest definition of alienation, since human beings have loaded their human qualities to some objects by absorbing them from himself, he now becomes objectified and glorifies these objects over time, enters their sovereignty and enslaves them (Fromm, 1997). The exchange value of commodities does not remain in the economy, but infiltrates into the purest feelings of human existence.
In this way, human relations are reified. Because an alienated mind objectifies everything he has experienced.
Whereas freedom doesn't begin under obligations, even it begin where obligations end. Tiny sparrows are the emulation of this freedom.