Then started with birds (4)
I believe the answer is:
hens
'birds' is the definition.
(hen is a type of bird)
'then started with' is the wordplay.
'with' indicates the answer is hidden within the clue.
'HENS' is hidden in the letters of 'then started'.
(Other definitions for hens that I've seen before include "Female fowl" , "Female chickens" , "Birds kept for laying" , "Adult chickens" , "Poultry" .)