Artist climbing inside bird colony of fast breeders (6)
I believe the answer is:
warren
'colony of fast breeders' is the definition.
'warren' can be an answer for 'colony' (I've seen this before). I'm not certain of the 'of fast breeders' bit.
'artist climbing inside bird' is the wordplay.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'climbing' is a reversal indicator (in a down clue, letters climb up).
'inside' is an insertion indicator.
'bird' becomes 'wren' (wren is a kind of bird).
'ra' in reverse letter order is 'ar'.
'ar' put within 'wren' is 'WARREN'.
Can you help me to learn more?
(Other definitions for warren that I've seen before include "Rabbit colony" , "Rabbit burrow" , "In Hastings, for example," , "Network of underground tunnels built by rabbits" , "Labyrinth of burrows" .)