Birds sound contented mostly, finding flowering plant (8)
I believe the answer is:
larkspur
'flowering plant' is the definition.
(larkspur is a kind of flowering plant)
'birds sound contented mostly' is the wordplay.
'birds' becomes 'larks' (lark is a kind of bird).
'sound contented' becomes 'purr' (I've seen this before).
'mostly' means to remove the last letter (most but not all of the word).
'purr' with its final letter taken off is 'pur'.
'larks'+'pur'='LARKSPUR'
'finding' is the link.
(Other definitions for larkspur that I've seen before include "Flower like a delphinium" , "Cultivated plant of the genus Delphinium" , "in bed!" , "Garden flower of delphinium family" , "Blue flower" .)