In a novel deeply concerned with what it means to be free, animals represent the various forms of incarceration. The first animal we see is White Dog, a completely domesticated animal that relies completely on the family for sustenance. White Dog trusts the woman, his provider, so much that he offers no resistance when she kills him out of mercy. Here, White Dog represents many of the Japanese-Americans themselves, who trust the U.S. government so much that they consent to the injustice of being sent to the internment camps.
Unlike White Dog, the family’s caged bird does escape its imprisonment. It is the family’s domesticated pet, but the woman decides to releases the bird from its cage instead of killing it, because she knows it can survive in the wild. When she first lets it out, however, the bird refuses to be free, tapping on the windows to be let back in. Here, we see the psychological power of incarceration, and the feeling of safety and security that can come with imprisonment. The bird has internalized its status as a prisoner and does not want to give it up—the cage is comforting and familiar to it.
Finally, the wild mustangs that the children see on the desert plain represent complete liberty. Running across the plain, the wild animals revel in their freedom. Looking out the window, the boy admires and longs for that freedom as his family hurdles toward the prison camp. For the boy, the horses represent that ideal state of freedom, which he will long for throughout the novel but never attain.