It's rather interesting that despite being such an old zoo with so many species, Milwaukee doesn't have very many "former" exhibits. Most of the zoo that was built many decades ago still stands today. Despite this, there are a ton of species that have come and gone throughout the years. A good chunk of the zoos central outdoor area is still labeled Africa/Asia/South America, so to avoid any confusion I will be dividing the three into their own lists. Also, I am not aware of the dates many of these species were phased out so please forgive me for the lack of info on that front.
Adventure Africa:
Yellow-backed Duiker
Africa Exhibits:
Giant Eland
Goliath Heron
Grant's Gazelle
Kori Bustard
Secretary Bird
Springbok
White Rhino
Asia Exhibits:
Asian Black Bear
Asian Elephant
Axis Deer
Blackbuck
Indian Rhino
Malayan Tapir
Sarus Crane
South America Exhibit:
Capybara
Cosoroba Swan
Giant Anteater
King Vulture
Lowland Paca
Patagonian Cavy
Various Macaw and Parrot Species
North America:
American Bison
American Black Bear
Black-tailed Prairie Dog
Dall Sheep
Great-Horned Owl
Moose
Polar Bear
Sandhill Crane
Steller's Sea Lion
Timber Wolf
White-tailed Deer
Wolverine
Australia (Former Exhibit):
Bennet's Wallaby
Emu
Red Kangaroo
Matschie's Tree Kangaroo
Koala
Turkey (Species Unknown)
Big Cat Country:
Amur Leopard
Caracal
Cougar
Monkey Island:
Rhesus Macaque
American Mink
Aviary:
Adelie Penguin
Black-crowned Night Heron
Black-necked Swan
Fulvous Tree Duck
King Penguin
Red-Billed Pintail
Primates of the World:
Barbary Ape
Black Macaque
Brown Stump-tail Monkey
Crested Mangabey
Debrazza's Monkey
Diana Monkey
Gelada
Lar Gibbon
Lion-tailed Macaque
Proboscis Monkey
Patas Monkey
Red Uakari
Sclater's Guenon
Skye's Guenon
Spectacled Langur
Tufted Capuchin
Reptile and Aquatics Center:
African Rock Python
Alligator Snapping Turtle
Amazon River Dolphin
American Alligator
Basilisk
Green Anaconda
Indan Rock Python
Russel's Viper
Water Monitor Lizard
Small Mammal House (Daylight Room):
Bat Eared Fox
Black-backed Jackal
Douroucouli
Dwarf Mongoose
Fisher
Grison
Jaguarundi
Meerkat
Rock Hyrax
Squirrel Monkey
Tayra
Tree Shrew
Small Mammal House (Nocturnal Room):
Binturong
Bush-tailed Galago
Ferret Badger
Genet (Species Unknown)
Giant Pangolin
Hog Badger
Kinkajou
Masked Palm Civet
Pale Fox
Palm Civet
Pygmy Slow Lorris
Adventure Africa:
Yellow-backed Duiker
Africa Exhibits:
Giant Eland
Goliath Heron
Grant's Gazelle
Kori Bustard
Secretary Bird
Springbok
White Rhino
Asia Exhibits:
Asian Black Bear
Asian Elephant
Axis Deer
Blackbuck
Indian Rhino
Malayan Tapir
Sarus Crane
South America Exhibit:
Capybara
Cosoroba Swan
Giant Anteater
King Vulture
Lowland Paca
Patagonian Cavy
Various Macaw and Parrot Species
North America:
American Bison
American Black Bear
Black-tailed Prairie Dog
Dall Sheep
Great-Horned Owl
Moose
Polar Bear
Sandhill Crane
Steller's Sea Lion
Timber Wolf
White-tailed Deer
Wolverine
Australia (Former Exhibit):
Bennet's Wallaby
Emu
Red Kangaroo
Matschie's Tree Kangaroo
Koala
Turkey (Species Unknown)
Big Cat Country:
Amur Leopard
Caracal
Cougar
Monkey Island:
Rhesus Macaque
American Mink
Aviary:
Adelie Penguin
Black-crowned Night Heron
Black-necked Swan
Fulvous Tree Duck
King Penguin
Red-Billed Pintail
Primates of the World:
Barbary Ape
Black Macaque
Brown Stump-tail Monkey
Crested Mangabey
Debrazza's Monkey
Diana Monkey
Gelada
Lar Gibbon
Lion-tailed Macaque
Proboscis Monkey
Patas Monkey
Red Uakari
Sclater's Guenon
Skye's Guenon
Spectacled Langur
Tufted Capuchin
Reptile and Aquatics Center:
African Rock Python
Alligator Snapping Turtle
Amazon River Dolphin
American Alligator
Basilisk
Green Anaconda
Indan Rock Python
Russel's Viper
Water Monitor Lizard
Small Mammal House (Daylight Room):
Bat Eared Fox
Black-backed Jackal
Douroucouli
Dwarf Mongoose
Fisher
Grison
Jaguarundi
Meerkat
Rock Hyrax
Squirrel Monkey
Tayra
Tree Shrew
Small Mammal House (Nocturnal Room):
Binturong
Bush-tailed Galago
Ferret Badger
Genet (Species Unknown)
Giant Pangolin
Hog Badger
Kinkajou
Masked Palm Civet
Pale Fox
Palm Civet
Pygmy Slow Lorris