this image seemed to portray the blend of two opposite feelings or emotions. placing one's self in the bird's position, one wouldnot know whether to feel sorry for her still-caged self.. or....to feel happy for her hitherto cage-mate's new-found freedom. it would certainly be a mix of contrary feelings tearing on the opposite directions.
and.... one important point to note in khalil's composition is....how his FATHER'S SLAVES had captured and enslaved a MIGHTY LION to amuse his father. SLAVES READILY MAKE OTHERS SLAVES, IN ORDER TO GRATIFY THEIR MASTER'S DIRTY WISHES, thus attempting to make themselves dear to their master and become his favourite. is it not natural a hunter would certainly like his capable hunting dog!? this seems to perfectly match with the indian scenario of caste system, in which, in my view, middle positioned caste people try to keep the lower caste people forever below them in stature, despite being hated(or...certainly not-loved) by the people from upper castes; notwithstanding that, middle caste people fawn on upper-caste people. this is how slaves put the naive people in double/triple/multi-layered slavery.
one more aspect is... the weak bird -though songless-addressing the stronger lion as her brother. anyone who can fight for freedom, for themselves and/or for others, is naturally regarded by the weak as a brother/protector/saviour. fellow feeling brings about the brotherhood in this shared trouble.
....another point that i should not forget to mention is... that the lion is brought into A GARDEN from A DESERT. in this garden he's sure to get a good food and safety and security, but at the loss of his freedom; in the desert's wilderness, he'd lead a life full of challenges and hardships. it remains a choice for one, what he'd choose to sacrifice and what he'd choose to go with.
regards.