Birds show pleasure endlessly, finding flowering plant (8)
I believe the answer is:
larkspur
'flowering plant' is the definition.
(larkspur is a kind of flowering plant)
'birds show pleasure endlessly' is the wordplay.
'birds' becomes 'larks' (lark is a kind of bird**).
'show pleasure' becomes 'purr' (I've seen this before).
'endlessly' means to remove the last letter.
'purr' with its last letter taken off is 'pur'.
'larks'+'pur'='LARKSPUR'
'finding' is the link.
(Other definitions for larkspur that I've seen before include "Blue flower" , "Mediterranean plant of the buttercup family" , "Mediterranean plant with spikes of blue, pink or white flowers" , "Flower like a delphinium" , "it grows" .)