Small seabird in the back of boat (5)
I believe the answer is:
stern
'back of boat' is the definition.
'stern' can be an answer for 'back' (stern means the back of a boat). I am not sure about the 'of boat' bit.
'small seabird' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'seabird' becomes 'tern' (tern is a kind of seabird).
's'+'tern'='STERN'
'in the' acts as a link.
Can you help me to learn more?
(Other definitions for stern that I've seen before include "at the back of the galley!" , "Hard - back" , "enforcing submission" , "Strict, austere" , "Unrelenting at the back of the boat?" .)