What is the Central Idea of this poem?

“Caged Bird”
by Maya Angelou

The free bird leaps
on the back of the wind
and floats downstream
till the current ends
and dips his wings
in the orange sun rays
and dares to claim the sky.

But a bird that stalks
down his narrow cage
can seldom see through
his bars of rage
his wings are clipped and
his feet are tied
so he opens his throat to sing.

The caged bird sings
with fearful trill
of the things unknown
but longed for still
and his tune is heard
on the distant hill
for the caged bird
sings of freedom

The free bird thinks of another breeze
and the trade winds soft through the sighing trees
and the fat worms waiting on a dawn-bright lawn
and he names the sky his own.

But a caged bird stands on the grave of dreams
his shadow shouts on a nightmare scream
his wings are clipped and his feet are tied
so he opens his throat to sing

The caged bird sings
with a fearful trill
of things unknown
but longed for still
and his tune is heard
on the distant hill
for the caged bird
sings of freedom.