Read the following passage from "The Caged Bird.”

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.

Based on the passage, what is the literal meaning of stalks?

the stem or main axis of a plant
the slender supporting part of anything
to pursue or approach prey stealthily
to walk with measured, stiff strides