Trafalgar Square bird (6)
I believe the answer is:
pigeon
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">trafalgar square bird</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for pigeon that I've seen before include "a visitor to Trafalgar Square" , "Common bird, wild and domesticated" , "run, perhaps" , "Common city bird" , "Dupe" .)