Jet surpasses birds (9)

I believe the answer is:

blackcaps

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

'birds' is the definition.
(blackcap is a kind of bird)

'jet surpasses' is the wordplay.
'jet' becomes 'black' (similar in meaning).
'surpasses' becomes 'caps' (I can't justify this - if you can you should give a lot more credence to this answer).
'black'+'caps'='BLACKCAPS'

Can you help me to learn more?

(Other definitions for blackcaps that I've seen before include "they have beaks" , "Judges used to have them" .)

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.