Do other birds retreat from this one? (4)
I believe the answer is:
skua
'do other birds retreat from this one?' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
This is all the clue.
Can you help me to learn more?
(Other definitions for skua that I've seen before include "Predatory northern seabird" , "Large relative of the gull" , "Arctic seabird" , "Brownish sea bird" , "Gull-like rapacious bird" .)