An aquatic bird to avoid? (4)
I believe the answer is:
duck
I believe this clue is a double definition.
'an aquatic bird' is the first definition.
(duck is a kind of aquatic bird)
'avoid?' is the second definition.
(duck can mean to avoid)
'to' is the link.
(Other definitions for duck that I've seen before include "sails material" , "Water bird - get out of the way" , "Water bird; zero score" , "eg Jemima, Donald" , "Score of nought in cricket" .)