KARATSU, Saga Prefecture--When a photovoltaic power station operator found a spate of expensive solar panels here broken by stones, the culprit initially remained a mystery.

A total of seven panels, each priced at more than 100,000 yen ($920), were broken over two years since they were set up in a mountainous area here in 2017.

Japan Environment Techno Co., based in Saga, reported the damage to police in July 2017, resulting in an on-site inspection by police.

President Mitsuharu Komuro, 51, said the panels were destroyed in a strange fashion.

Some were located where it is difficult for humans to damage them by throwing stones, while fragments of a rice bowl were found nearby in other cases.

The company operates 30 solar power plants in and outside Saga Prefecture, but such damage was reported only at the Karatsu facility.

After repeatedly visiting the site, company officials realized that hundreds of crows flying overhead probably dropped stones. The birds are known to drop walnuts, shellfish and other food from the sky to crack them to eat.

In March, Japan Environment Techno learned about a device to scare crows away produced by Eco-5, a Saga-based company. It generates the cries of crows being attacked, as well as the calls of its natural enemies such as hawks and eagles, through the amplifier and loudspeaker.

The company tested the equipment at the plant, seeing 20 to 30 crows flying away from nearby electric cables and utility poles.

No damage to solar panels has been reported since a total of eight devices were installed in April.

Yoichi Nagano, 65, president of Eco-5, said he was surprised at the order from the power generator.

“We have engaged in the development of sound-based equipment for seven years,” said Nagano. “Most of our customers are fruit farms, ‘nori’ makers and other agricultural and fisheries operators, and it was the first time for receiving an order from a solar power producer.

“I did not know so serious damage has been reported (at a solar power plant).”

Komuro said he does not feel completely at ease over the issue.

Fearing that crows may become accustomed to the sound deterrent, Komuro plans to fly a drone mounted with a small anti-bird device once or twice a month to nearby forests crows inhabit to threaten the birds with noise.

“Crows are smart,” said Komuro. “They will return when we forget about their existence. I do not want to kill animals. I would like to fight a battle of wits in a spirit of coexistence and co-prosperity.”