By Allison Love, CNN
Updated 1241 GMT (2041 HKT) December 30, 2015
During the 1960s, many Japanese people owned pets for the first time. Tropical birds like Mizutani's parakeets were brought to the country from places such as India and Sri Lanka. The feral birds Mizutani encountered are the descendants of the former pets.
Despite the challenges of photographing wild animals, Mizutani began to understand more about the parakeets and their relationship with their environment.
"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," he said.
Mizutani's photos have an eerie quality to them and convey the feelings of fear he experienced when he first encountered the birds.
Yoshinori Mizutani spent a year photographing wild parakeets that can be found in 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.
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.
(CNN)Every morning in Tokyo's Setagaya ward, flocks of parakeets would fly to an elm tree near Yoshinori Mizutani's home.
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.