Bird having a plaintive warble initially in heather (7)
I believe the answer is:
lapwing
'bird' is the definition.
(lapwing is a kind of bird)
'a plaintive warble initially in heather' is the wordplay.
'initially' suggests taking the first letters.
'in' is an insertion indicator.
'heather' becomes 'ling' ('ling' can be a synonym of 'heather').
The first letters of 'plaintive warble' is 'pw'.
'a'+'pw'='apw'
'apw' inserted within 'ling' is 'LAPWING'.
'having' acts as a link.
(Other definitions for lapwing that I've seen before include "Crested plover" , "Variety of plover" , "Plover, pewit" , "Green plover" , "Bird of the plover family" .)