Bird beginning to roost on old rubbish receptacle (5)
I believe the answer is:
Here is my best explanation:
'bird' is the definition.
(robin is a kind of bird)
'beginning to roost on old rubbish receptacle' is the subsidiary indication.
'beginning to' suggests taking the first letters.
'on' means one lot of letters go next to another.
'old' becomes 'o'.
'rubbish receptacle' becomes 'bin' (I've seen this before).
The initial letter of 'roost' is 'r'.
(Other definitions for robin that I've seen before include "Small songbird", "Man's name", "Batman's assistant", "Hood, Goodfellow or redbreast?", "Redbreast", "Red-breasted songbird", "Christmas-card bird", "See 7", "Batman's helper" and "Small brown thrush".)