Learn Swedish: Djuren förflyttar sig mot söder på hösten. - The animals move towards the south in the autumn.

Flyttar usually means moving to a new residence (like moving house), while rör sig just means physical motion (like moving a body part or walking around). Förflyttar sig specifically means transporting or relocating from one place to another, making it the perfect choice for migrating animals.

Could I say söderut instead of mot söder here?

Yes, absolutely! Söderut means "southwards." Saying förflyttar sig söderut is very natural and means practically the same thing as förflyttar sig mot söder (move towards the south).

Why is it på hösten and not i hösten?

In Swedish, you use the preposition på with the definite form of a season to talk about something that happens regularly during that time of year (like a recurring migration). The preposition i is used for specific instances: i höst means "this coming autumn" and i höstas means "last autumn."

Is söder a noun or an adjective in this sentence?

Here, söder is a noun meaning "the south." If you wanted to use an adjective to describe something as southern, you would use södra, as in södra Sverige (southern Sweden).