Meaning: Birds travel to warmer areas when it gets cold.
Choice of Words: Birds: flying animals; fly: move through the air; south: direction opposite of north; winter: cold season.
Alternative Expressions
The birds are going to the warmer place for the cold season.
Meaning: The birds are migrating to a warmer location to escape the harsh winter conditions.
Choice of Words: The birds are the subject of the sentence and are described as "going" to a warmer place. "Warmer place" refers to a location with a more favorable climate. "Cold season" is another way to refer to winter.
Birds travel to the southern region during the chilly time of the year.
Meaning: The birds are migrating to a warmer region during the winter months.
Choice of Words: Birds are the subject of the sentence and are described as "traveling" to a southern region. "Southern region" refers to the area below the equator. "Chilly time of the year" is a poetic way to refer to winter.