BIRDS
There were originally 7 of these Japanese-style aviaries, constructed in 1875. In 1974 6 of them were demolished with the 7th being preserved as a memorial to Martha, the last known passenger pigeon.
These are not postcards

Martha
Aviary in
1974
Martha's Pavilion-1984
Passenger (carrier) pigeons were once the most numerous bird species on the planet with around 1 billion birds. The last known colony was reported in Michigan. When Martha arrived at the zoo in 1902 she was one of the few remaining carrier pigeons. The species had been ruthlessly slaughtered between 1880-1900 by hunters who used them for food and for live targets. The Cincinnati Zoo, in a desperate attempt to help replenish the species, offered $1,000 for a mate for Martha, but none could be found. The 3rd non-postcard image above is one of the 5 original bird aviary buildings that were built in 1875. Martha died in one of these buildings Sept. 2, 1914 and it is now a memorial to her and to Incas the last Carolina Parakeet which also has disappeared from the planet. Martha died when she was an old and frail 29 year old bird. Her body was packed in 300 lbs of ice and sent to the Smithsonian Institution in Washington D.C. where it remains today.

Eagle
cage
Aquila (eagle)
Trained
Eagle Brownie & owner
Betsy Ross and Brookfield Baldy, the pair of Bald Eagles at the zoo, produced an eaglet which was later released in the wild. The release was part of a program aimed at increasing the population of the endangered species.

White
Peacock
RP of Storks on
nest
You name them
ELEPHANTS
Many of these early cards show a female Asian elephant named "Hatnee" who was a favorite of zoo visitors for decades. She frequently gave rides to children while being led by her trainer, Ed Coyne. Ed started at the zoo when he was 10 years old in 1877 and was still working there 65 years later when he died in 1942. He is seen standing on the leg of the elephant in the 1st non-postcard image below, and standing in front of the Asian elephant in the other.

Zoo Keeper Ed Coyne around 1915

Gimpy-A Pigmy Elephant
Photo by Paul Briol
Gimpy was donated to the zoo in 1932 by Judge Alfred K. Nippert. She was only 6' tall at maturity and was one of the most popular attractions at the zoo for many years.