Answer:
The Birds flew south to their winter home.
Explanation:
When you study basic English Grammar one of the first topics is  the personal pronouns:
I Â ( Singular)
You ( Singular or plural)
He ( Singular)
She ( Singular)
It  ( Singular)
We (Plural)
They  (Plural)
The Pronoun The birds must be substituted by They flew south.....