Second heron bothered smaller waterbird (7)
I believe the answer is:
moorhen
'smaller waterbird' is the definition.
'moorhen' can be an answer for 'waterbird' (I have seen 'Black waterbird ' mean 'moorhen' so perhaps 'waterbird' could also mean 'moorhen'). I'm not certain of the 'smaller' bit.
'second heron bothered' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'bothered' is an anagram indicator.
'heron' with letters rearranged gives 'orhen'.
'mo'+'orhen'='MOORHEN'
Can you help me to learn more?
(Other definitions for moorhen that I've seen before include "Water bird" , "Black freshwater bird" , "Bird - hormone (anag)" , "Female red grouse or waterfowl" , "Black waterbird" .)