Penguin's cousin (3)
I believe the answer is:
auk
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">penguin's cousin</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 auk that I've seen before include "Black-and-white diving bird of northern seas" , "Black-and-white seabird" , "Great ---, extinct seabird" , "Diving sea bird" , "One that flies" .)