Crossword Genius

You'll find him in probing a book of birds (5)

Ross

I believe the answer is:

robin

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

'you'll find him' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'probing a book of birds' is the wordplay.
'ROBIN' is hidden within the letters.
But, I'm uncertain how the hidden word is indicated.

'in' acts as a link.

Can you help me to learn more?

(Other definitions for robin that I've seen before include "Day was one" , "See 7" , "Batman and --" , "Small songbird" , "Bird - one in Lincoln green?" .)

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