Sun had crow joining in early performance (4,6)
I believe the answer is:
dawn chorus
'early performance' is the definition.
The definition suggests a singular noun which matches the answer.
'sun had crow joining' is the wordplay.
'sun had crow' anagrams to 'DAWN CHORUS'.
But, I'm not clear how this is indicated.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for dawn chorus that I've seen before include "Birdsong" , "Early morning sing-song?" , "Early sound of birds" , "Bird song at daybreak" , "singing, naturally" .)