Breakdown of Осенью птицы летают на юг.
птица
bird
на
on, at / by (transport) / to (a place) / to (in answer to)
осенью
in autumn
юг
south
Questions & Answers about Осенью птицы летают на юг.
Why does this sentence use летают instead of летят?
The verb летают is a multidirectional verb of motion. It is used here because the birds flying south is a repeated, habitual action that happens every autumn. It works just like ходить (to go by foot habitually) compared to идти (to be walking right now).
Why does the word for 'in autumn' (осенью) end in -ю instead of using a preposition like в?
To say an action happens in a specific season, Russian uses a special grammatical form called the instrumental case. The word осень (autumn) becomes осенью. You do not need a preposition like в (in); the ending handles the meaning all by itself.
Why do we use the preposition на in на юг instead of в?
In Russian, compass directions like юг (south) and север (north) always take the preposition на when you are talking about traveling towards them.
What grammatical case is юг (south) in this sentence?
It is in the accusative case because it is the destination of the motion. Since юг is a masculine noun that is inanimate (not a living thing), its accusative form looks exactly like its basic dictionary form.