The parakeets, an uncommon sight in Japan with their bright-green feathers and scarlet beaks, caught the photographer's attention. As he noticed the birds each day, more and more began to arrive until there were hundreds of parakeets.
Mizutani was struck by shock and fear at seeing so many.
"I felt as if I'd walked into the Alfred Hitchcock film 'The Birds,' " he said.
Mizutani researched the parakeets and learned there was a large nest in one of Tokyo's suburbs, Ookayama. He visited the site, inhabited by hundreds of birds, and started photographing them.
During the 1960s, many Japanese people owned pets for the first time. Tropical birds like Mizutani's parakeets were brought to Japan from places such as India and Sri Lanka.
The parakeets didn't make for great pets, however. They were noisy, and many were consequently released by their owners. The feral birds Mizutani encountered are the descendants of the former pets, and as their population has increased, they've made their home in areas of Tokyo and other parts of Japan.
For Mizutani, the colorful parakeets are incongruous with Tokyo's urban environment. Normally, birds of this nature couldn't survive in a climate like Tokyo's. But they have adapted to the cold -- a feat Mizutani finds striking.
"I had an uncanny feeling when I first saw them," he said. "I decided to work on 'Tokyo Parrots,' a project that captures a surreal and extraordinary urban landscape."
Mizutani chose to photograph the birds with a strobe light. Without the light, he said, their vivid color would be lost and the birds would appear as a dark shadow in the sky when photographed from below. In order to get close-up shots, Mizutani photographed the parakeets from buildings, all the while fearing he could be attacked.
The resulting images have an eerie quality to them and convey the feelings of fear Mizutani experienced when he first encountered the birds. In one image, dozens of lime-green parakeets fly through a purple sky and out of the frame. In another photo, they're perched together at the top of a tree. The birds seem out of place against a modern cityscape.
Mizutani worked on his series for a year and, despite the challenges of photographing wild animals, he began to understand more about the parakeets and their relationship with their environment. This understanding shaped the outcome of his project.
"(The) parakeets live in ginkgo trees, and I wanted to capture them with the changing background of the four seasons, especially with the ginkgo leaves turning yellow in autumn," he said. "I learned that they change the tree on which they build nests and the time and direction they take to return home depending on the season."
As Mizutani noticed ways in which the parakeets have adapted to life in Tokyo, he also discovered ways the people of Tokyo have adapted to the birds' presence.
"I paid more attention to (the birds') surroundings and noticed some traces of struggle between the native human and the foreign creature," he said. He saw electric wire on fences to keep out the parakeets and even witnessed people running away from their nests.
"These parakeets aren't supposed to exist in Tokyo, but they do," Mizutani said, acknowledging there is beauty in the unusual.