This year beehives from rural areas were relocated to the top of a large water-treatment facility near Tokyo's international airport, where as many as 4,000 birds known as little terns nest after a long migration from Australia, New Zealand, and Papua New Guinea.
Although they are not endangered internationally, little terns are listed as "vulnerable" in Japan's Red Data Book of threatened species.
That's because the terns' nesting sites in the country are being destroyed by construction work and other human activities, so the birds are considered potentially at risk in the future.
The terns near the airport have long been victims of Tokyo's crows.
In a single prolonged attack five years ago, about 60 crows picked off roughly 300 eggs and 160 young birds, and fewer terns have come to the nesting site since then.
"The young can't defend themselves against the crows, so we tried to find ways to protect them at the nesting site," said Naoya Masuda, a member of the nonprofit Little Tern Project.
"One thing we tried was putting netting in the trees and stringing up fishing lines, but nothing worked."
Then a suggestion from a city water-bureau employee led the tern group to the Ginza Bee Project.
The Tokyo-based nonprofit, launched in March 2006, keeps hives in the upscale Ginza shopping district to educate urbanites about agriculture.
About 150,000 bees living high above the store-studded streets collect pollen from city plants, including from the grounds of the Imperial Palace and nearby Hibiya Park. (See photos of the Imperial Palace.) As part of the project, the group sells about 660 pounds (300 kilograms) of honey each year, invites groups up to visit the hives, and take notes on unusual bee behaviors.
According to group chair Kazuo Takayasu, their observations suggest that using bees to battle crows will turn out to be an effective solution.
"We spoke to an expert and learned that honeybees in the wild have the natural response of attacking a black object that comes near to their hive," Takayasu said.
"There have been tests with black and white balloons, and the bees always attack the black balloon."
It is believed that the bees' reaction is linked to the color of bears' fur. The insects apparently attack dark-colored creatures to protect their hives from plunder.
"We noticed that the bees swarmed around crows that were taking offerings from white plates left on the outdoor altar of a shrine in Ginza," Takayasu added.
(Read related news: "Bee Buzz Scares off African Elephants" [October 9, 2007].)
"After a while the crows stopped coming back, so we thought it was worth trying at the terns' nesting site."
Between July and November of last year, two hives were placed on the roof of the Morigasaki Water Reclamation Plant to protect the birds once they arrived in April, and another hive was added this May.
Around 20,000 honeybees currently patrol the terns' nests, according to Masuda of the Little Tern Project, who added that the two creatures are getting on "like good neighbors."
"It is not 100 percent foolproof yet, because the area is quite large, and there do seem to have been fewer birds here this year so far," he said.
"But we are hopeful that it will prove effective over the long term."