cage is like a prison cage is the like prison in which we keep some one not on his own choice but our own choice usually we kept the birds in the cage  

bird has also wishes like the human being they also want to enjoy there life they want to fly in the air they want to share there feeling with there friends as when we are in the prison we feel that there would be death in the next moments our time is not passed there we thing that what the time become we set free and we will enjoy our life

the same situation is like with the birds they do not want to live in the cage they wanted to set free as our wishes so it is upon us that we ignore these thing we will get the birds free so that they will enjoy there life