Songbird enveloped at first in brightly-coloured flags (4,7)
I believe the answer is:
reed bunting
'songbird' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'enveloped at first in brightly-coloured flags' is the wordplay.
'at first' suggests taking the first letters.
'in' is an insertion indicator.
'brightly coloured' becomes 'red' (red is often a bright colour).
'flags' becomes 'bunting' (I've seen this before).
The initial letter of 'enveloped' is 'e'.
'e' put into 'red' is 'reed'.
'reed'+'bunting'='REED-BUNTING'
Can you help me to learn more?
(Other definitions for reed bunting that I've seen before include "Bird breeding in marshes" , "Bird, the male with black head and white collar" , "Flier" , "singer" , "Bird of marshes and hedgerows" .)