Non-Pooped on Statues
April 3, 2004
Fending off annoying birds
Asami Nagai / Daily Yomiuri Staff Writer
When Kanazawa University chemist Yukio Hirose accepted the Ig Nobel Prize in Chemistry at Harvard in 2003, he surprised the audience by thanking the pigeons and crows of his hometown. His joke landed beautifully, but the backstory is earnest: decades earlier, he’d wondered why a particular bronze statue in Kanazawa never attracted birds. That old curiosity eventually led him to develop a bird‑repellent bronze alloy, a discovery that became unexpectedly relevant as urban bird problems—and later bird flu—intensified.
Media coverage of his alloy brought a flood of inquiries, including one asking if he’d like to be nominated for the Ig Nobel, a prize that celebrates research that “first makes people laugh, then makes them think.” Initially skeptical, Hirose came to appreciate that the award honors practical, public‑minded ingenuity, even when wrapped in humor. His one-minute acceptance speech—complete with a planned $1 tip to the timekeeper—won over the crowd, who laughed at nearly everything he said.
Since winning, Hirose has been inundated with requests from people desperate for ways to keep birds away. He jokes that this sudden fame is the most exhausting part of the honor, but the underlying truth is clear: his quirky line of inquiry turned out to be unexpectedly useful.
Tenacity leads to development
Hirose is not an ornithologist but a material scientist. At age 18, while studying engineering as a first-year student at Kanazawa University, he began wondering how a statue in Kenrokuen, a park near the university back then, managed to remain completely clean of pigeons’ droppings, while nearby trees and other statues were usually painted white with them.
Visiting the park frequently for various reasons, Hirose came to realize that this statue of Prince Yamato Takeru, built in 1880, attracted few, if any, birds. “I used to come to the park to party or nap, and found there were lots of birds perched around there,” Hirose said. “But they always seemed to prefer tree branches to the statue’s head and shoulders, which I found very strange.”
At that time, he did not try to investigate the cause. But he unexpectedly returned to the problem when, as a metal fatigue expert, he was given an opportunity to study the statue’s materials when it was pulled down for repair work in 1989. On the 5.5-meter bronze statue, Hirose found no white splotches, again making him ponder why.
As he investigated the composition of the material, he recalled a statement in the book, Studies in Ancient Technology, by R.J. Forbes. Hirose was responsible for translating Chapter 5, which deals with elements that include antimony and arsenic. The statement he read was about how arsenic is lethal to birds.
The moment Hirose discovered the high content of arsenic in the statue, he was almost positive that this was what was driving the pigeons away.
“Unlike the Yamato Takeru statue, Takamori Saigo’s statue in Ueno Park, Tokyo, is stained badly with droppings,” Hirose said. “The arsenic content in the Saigo statue is 2 percent to 3 percent, while the alloy used in the Yamato Takeru statue contains more than 10 percent arsenic.” In fact, the content is not even. It is 2 percent at the head but reaches as much as 15 percent at the feet. Further research showed that that the high arsenic content helped the bronze alloy melt at 1,000 C, compared to the 1,300 C needed to melt bronze with a 2 percent arsenic content. When the Kanazawa statue was built, around 1880, artisans who had access to only relatively primitve furnaces had no choice but to mix a lot of arsenic with the bronze to be able to create a bronze statue.
Nearly 10 years after making the connection between birds and arsenic, Hirose finally had a chance to implement his theory. About a year ago, Hirose, then the director of his alma mater’s Cooperative Research Center, met with a local businessman who came to see Hirose to ask whether he knew of an effective way to remove sticky flyers from walls and phone booths.
As this businessman turned his back, Hirose saw that his shoulders were dotted with a white substance, which turned out to be bird droppings. As it happened, the man was having a hard time with pigeons that congregated near his office.
By this time, many people had brought the issue of bird droppings to the center, hoping Hirose could offer a solution.
In response, he created copper alloy pieces that had a 10 percent arsenic content that also contained lead and tin as well as other elements. As a solid object, this alloy is perfectly safe. But if burned at higher than 1,000 C, a vapor containing arsenic–lethal, of course–is emitted. In other words, people who happen to inhale the vapor will instantly, in Hirose’s words, “be sent to the next world.” This discourages many town officials who are desperately seeking antibird measures.
“I was approached by Tokyo metropolitan government officials,” Hirose said. “When they learned that a fatal vapor could be created if there was a fire, they became hesitant about using the alloy. They said they couldn’t use it in any populated area, where fires very well could occur.”
Hirose risked his life in attempting to create the alloy. Assisted by one of his former students, he worked in a private lab he built on the land lot he owned, wearing a protective mask and a suit.
Even this precautionary measure, however, didn’t prevent Hirose from sometimes feeling a little queasy.
Having created the bronze, he placed pieces of it in a circle in front of JR Kanazawa Station, where pigeons usually flock.
Hirose videotaped the area around the circle for six hours a day. Not a single pigeon dared to come within a meter of the circle, despite their favorite food being scattered on the ground.
“It was amazing,” he said. “Pigeons squawked at the bronze, kind of like how a woman sniffs at a man she doesn’t like.” After he removed the plates, the birds came back to eat the food.
Next, he placed the bronze on the roofs of factories where numerous crows often gather, as well as in garbage piles and a cowshed. Crows chose to stay away from the metal plates.
Still, he needed to prove the bronze could be used safely. To do so, he chose several goldfish to be his guinea pigs. He left a piece of the bronze in a water tank for a month and kept several goldfish in it for a few more months. The fish all survived.
“The amount of toxic substance that escaped into the water from the bronze was 0.014 milligrams for every liter,” Hirose said. “This figure is far below the nation’s environmental standard of 0.3 milligrams. Even hot water at a nearby spa has a higher arsenic content.” But just to be on the safe side, he tested its safety one more time. “I rubbed the alloy onto some candy and ate it. But nothing serious has happened to me,” Hirose said matter-of-factly.
Arsenic
Although arsenic’s toxicity looms over the story, Hirose insists the alloy’s bird‑repelling power likely comes from subtler forces: its smell, its electromagnetic behavior, or the negative ions it emits. With its unusually high arsenic content plus elements like lead and silicon, the bronze behaves like a semiconductor. When light strikes it, Hirose explains, it generates a faint electric current—something he suspects birds can sense and instinctively avoid.
He also measured roughly 1,000 negative ions per square meter emanating from the alloy. While small amounts of negative ions are often touted as beneficial, Hirose believes the high concentration around the bronze may be aversive to birds.
His curiosity didn’t stop at metals. He requested four captured crows from city workers and spent months experimenting with them in a cage. One unexpected finding: crows dislike blue LED light. When he shone blue light on them, they tried to flee. That observation nudged him toward safer, non‑arsenic bird‑repellent technologies, including a net woven with materials that generate large amounts of negative ions.
Hirose jokes that even with an Ig Nobel Prize, he hasn’t given up on the “real” Nobel. He’s already eyeing other universal human problems—athlete’s foot and balding—with mock confidence. “Whoever finds the ultimate cure will win a Nobel Prize,” he says. “And I’m very close.”