Can You Help Me Interpret "Fable For When There's No Way Out" By May Swenson?

Grown too big for his skins,
and it gown hared,
without a sea and atmosphere-
he's drunk it all up-

Grown too big for his skin,
and it grown heard,
without a sea and atmosphere-
he's drunk it all up-
his strength's inside him now,
but there's no room to stretch.
He pecks at the top
but his beak's too soft;
though instinct or ambition shoves,
he can't get through.
Barely old enough to bleed
and already bruised!
In a case this tough
what's the use
if you break your head
instead of the lid?
Despair tempts him
to just go limp;
maybe the cell's
already a tomd,
and beginning end
in this round room.
Still, stupidly he pecks
and pecks, as if from under
his own skull-
yet makes no crack...
And kicks and stomps.
What a thrill
and shock to feel
his little gaff poke
through the floor!
A way he hand't known or meant
rage works if reason won't
when locked up, bear down