Birdbrain
I believe the answer is:
dodo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">birdbrain</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for dodo that I've seen before include "bird long dead" , "Flightless bird, extinct since the 17th century" , "Native of Mauritius" , "Proverbially extinct bird" , "silly person" .)