Feels sorry for river birds (7)
I believe the answer is:
regrets
'feels' is the definition.
(regretting is a kind of feeling)
'sorry for river birds' is the wordplay.
I cannot really see how this works, but
'river' could be 'r' (abbreviation) and 'r' is present in the answer.
'birds' could be 'egrets' (egret is a kind of bird) and 'egrets' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for regrets that I've seen before include "Sorrows" , "Rues" , "Bemoans" .)