Birds keep moving south to the other side (4)
I believe the answer is:
aves
'birds keep moving' is the definition.
'aves' can be an answer for 'birds' (I've seen this before). I'm unsure of the 'keep moving' bit.
'south to the other side' is the wordplay.
I cannot really understand how this works, but
'south' could be 's' (abbreviation) and 's' is found in the answer.
The remaining letters 'ave' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for aves that I've seen is " Reverential salutations: class of vertebrates which comprises birds".)