A bird seeking a mate? (4)

I believe the answer is:

rook

I'm a little stuck... Click here to teach me more about this clue!

'a bird' is the definition.
(rook is a kind of bird)

I cannot understand how the rest of the clue works.

(Other definitions for rook that I've seen before include "Rip off - bird" , "journalist Jean" , "Swindle; castle" , "Species of crow" , "Steal - castle" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.