It is more impressive than a birdie of course (5)

I believe the answer is:

eagle

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

'birdie of course' is the definition.
'eagle' can be an answer for 'birdie' (thesaurus). I am not certain of the 'of course' bit.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for eagle that I've seen before include "A glee-ful bird?" , "It may soar" , "ten-dollar coin" , "The emblem of the US is bald" , "King of birds" .)

I've seen this clue in The Globe and Mail.

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