Empty shores in which you'll see bird moves quickly (6)

'moves quickly' is the definition.
(I've seen this in another clue)

'empty shores in which you'll see bird' is the wordplay.
'empty' says to hollow out the word (remove centre letters).
'in which you'll see' is an insertion indicator.
'bird' becomes 'coot' (coot is a kind of bird).
'shores' with its centre removed is 'ss'.
'ss' placed around 'coot' is 'SCOOTS'.