Clamber about on branch (5)
I believe the answer is:
climb
'clamber' is the definition.
(thesaurus)
'about on branch' is the wordplay.
'about' becomes 'c' (circa).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'branch' becomes 'limb' (I've seen this before).
'c'+'limb'='CLIMB'
(Other definitions for climb that I've seen before include "Rise, mount" , "showing the way up" , "Ascend - ascent" , "Ascend, scale" , "Move upwards, ascend" .)