It would augment the zoo's total exhibits (5)
I believe the answer is:
adder
'it would augment the zoo's' is the definition.
The definition suggests a singular noun which matches the answer.
'total exhibits' is the wordplay.
'total' becomes 'add' (synonyms).
'exhibits' becomes 'er' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'add'+'er'='ADDER'
Can you help me to learn more?
(Other definitions for adder that I've seen before include "Dread (anag)" , "Type of snake" , "Totting snake" , "1 of 21 [SNAKES]" , "accountant?" .)