Disturbed doctor has a form of ennui being one who prefers a cold climate (7)
I believe the answer is:
penguin
'being one who prefers a cold climate' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Maybe there's a link between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for penguin that I've seen before include "Flightless marine bird" , "swimmer" , "Chocolate biscuit" , "paperback" , "Antarctic seabird with flippers for wings" .)