Songsters no end shy, internally tense on edges of copse (7)
I believe the answer is:
titmice
'songsters' is the definition.
The answer and definition can be both animals as well as being plural nouns.
Maybe you can see an association between them that I can't see?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for titmice that I've seen before include "Little singers" , "Small birds" , "little birds" , "Small, active songbirds" .)