A caged bird is a metaphor of budging thought ‘struggling like a bird’ in a human skull (see Plato).
All attention of the man in a cage is focused on the bird – he expects it to bring him news of the possible release from the prison:
“And like a death row criminal I'm looking around for a kindred spirit” (from the poem by Mikhail Lermontov).
This man does not have much of a choice – he has, as we see, only a certain Rat character for companion in his solitude. We know that there is a 90% coincidence between the human genome and the genome of a rat. However, in a time of crisis a man looks for a ‘kindred spirit’. We see him turning to the caged parrot for compassion: the parrot’s ability to mimic human speech was often symbolically associated with the gift of prophesy. In the Christian religion a bird in contact with divine spheres – the Dove in the Annunciation for example, delivering the long-awaited message from above.
Note also that the artist was using the method of inversion in the painting: a closer look reveals how the imprisoned and the observer are diagonally interchangeable and the darkness of the prison cell is replaced with all the glory of the blooming nature. And the bright-coloured bird, the landscape with a river that could take him to the ‘wonderful thereafter’ exists only as a figment of the prisoner’s imagination.