Penguin's cousin (3)
I believe the answer is:
auk
'penguin's cousin' is the definition.
(I've seen this in another clue)
This is all the clue.
(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" .)