I think it's a elephant.
Howler Monkey's have been known to be very loud, they may be the loudest in a specific zoo that contains Howler Monkey's but I am unsure about the general loudest animal in the zoo.
a chimpanzee who is loud by nature
lion
elephant
lion?
Lion
A lion roaring.
monkey, elephant, giraffe
Peacocks and lions and tigers.
elephants? i dont know why does it matter?
Well It's how you hear it. To me I would it is the elephant but if you are right next to a lion it may be loud.
The noun 'zoo' is a common noun, a general word for any establishment that maintains a collection of wild animals for study, conservation, or display to the public. A proper noun is the name of a specific person, place, or thing. A proper noun for the common noun 'zoo' is the name of the zoo, for example, The San Diego Zoo or The Beijing Zoo.