Small bird at rear of ship (5)
I believe the answer is:
stern
'rear of ship' is the definition.
(I've seen this before)
'small bird' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'bird' becomes 'tern' (tern is a kind of bird).
's'+'tern'='STERN'
'at' is the link.
(Other definitions for stern that I've seen before include "enforcing submission" , "Severe; grimly serious" , "Unsmiling" , "Strict; severe" , "Tail of a beagle" .)