Flocks of birds seen around Land's End (6)
I believe the answer is:
crowds
'flocks' is the definition.
'birds seen around land's end' is the wordplay.
'birds' becomes 'crows' (crow is a kind of bird**).
'seen around' is an insertion indicator.
'end' indicates one should take the final letters.
The final letter of 'land' is 'd'.
'crows' enclosing 'd' is 'CROWDS'.
'of' is the link.
(Other definitions for crowds that I've seen before include "Hosts" , "Presses" , "Hordes" , "Swarms" , "Large numbers of people" .)