Animals the zoo started with: wild bears (6)
I believe the answer is:
zebras
'animals' is the definition.
(I've seen this before)
'the zoo started with wild bears' is the wordplay.
'started with' indicates taking the first letters (I've seen 'start with' mean this).
'wild' indicates an anagram.
The initial letter of 'zoo' is 'z'.
'bears' is an anagram of 'ebras'.
'z'+'ebras'='ZEBRAS'
(Other definitions for zebras that I've seen before include "African striped animals" , "Striped horse-like animals" , "Black and white equines" , "Black and white striped animals" , "Striped beasts" .)