Dear Alice,

I live in rural Kyoto and am puzzled by what seems to be the local version of the scarecrow. They take plastic crows and hang them, usually upside down, on a string off a pole. I can't figure out what the heck the thinking is here. Is the idea to scare off crows by showing them what might happen to them?

John R., Kyoto

Dear John,

Your neighbors are using a relatively recent adaptation of a very old method of crow control, which is to string up a real dead crow and let it dangle til it rots.

This is not a practice particular to your neck of the woods. It's seen elsewhere in Japan and in a few other countries as well. The plastic version, which is made near Osaka and so far sold only in Japan, is easier to obtain, lasts longer, and is less likely to induce vomiting during installation.

The company that successfully commercialized the dead crow is Mitsugiron, a plastics manufacturer in Sakai City. I phoned up and spoke to Yoshihiro Morimoto in the sales department, who told me the company rolled out the crows eight years ago.

There are two models: the basic "Kowagarasu" (¥1,700 and shown in the photograph accompanying today's column) and the deluxe "Iyagarasu," which uses dyed duck feathers for a more realistic look (¥4,500). There's word play in those product names: "Kowagarasu" means "to frighten" but in its parts suggests "scary crow;" "Iyagarasu" means "to harass" but also sounds like "disgusting crow."

While sales aren't exactly soaring, they have been holding steady, according to Morimoto. He confirmed the idea is to frighten crows by making them believe there is something in the area so dangerous that the fellow on the stick fell victim.

But would a crow really fall for that? To find out, I got in touch with Shoei Sugita, a professor in the animal-science department at Utsunomiya University. He's written so many best-selling books on crows, and made so many television appearances, that he's popularly known as "Karasu Hakase" ("Professor Crow").

For the benefit of readers who live outside of Japan, I should explain why crows rate major media coverage here. It's because there are a lot of them — 20,000 to 30,000 in Tokyo alone — and they're big pests. Most of the crows in Japan are either hashibuto karasu (jungle crows, Corvus macrorhynchos) or hashiboso karasu (carrion crows, Corvus corone). Trust me when I say they're intimidating, especially when right overhead. They're black all over, including their bills, legs and feet, and average a whopping 50 cm in length.

In the countryside, crows descend on fields and eat up seed as fast as farmers can plant it. They also attack mature crops, with a special liking for grapes, pears and watermelon. According to the Ministry of Agriculture Forestry and Fisheries, crows caused an estimated ¥2.6 billion in agricultural losses in 2007, the most recent year for which figures are available.

In cities, crows rip open garbage bags looking for food, scattering trash and creating unsightly messes that are costly to clean up. They nest in crowded city parks, and then dive-bomb humans who come too close. Every spring there are numerous reports of crow attacks on both children and adults.

Crows also cause major trouble for utility companies when they nest on utility poles. As they build their nests, they drop nesting material on the unprotected junctures in electric lines, causing shorts that can set off widespread power outages.

But to migrate back to your question, I asked Sugita whether the birds would really be frightened by a crow dangling from a stick. That would depend, he said, on whether the crow is real or fake.

"Crows do seem to be affected by the death of one of their own, which is not true for all animals," he explained. "We've run experiments in which a healthy crow is suddenly confronted with a dead crow. In about 60 percent of the trials, the crow made an unusual cry which suggests it was feeling alarm or distress. So a real dead crow would probably work as a scarecrow, at least for a while."

Sugita didn't think the plastic decoy would fool a crow. "These are very smart birds," he commented. "They have much larger brains than chickens and ducks, for example, and can learn a human face in two or three days. They also have excellent vision, roughly five times better than humans, and a highly developed ability to distinguish colors. I believe a crow would have no trouble differentiating between a real dead crow and a plastic model, even at a distance and just by looking at it."

So a plastic crow would be no more effective than any other unfamiliar object?

"I've had farmers tell me that the plastic models work, but I suspect they just happened to place them well, and when the crows moved on they found a better place to feed. Otherwise, the crows would come back and watch the object for a few days, and once they saw that it posed no threat, it wouldn't bother them in the least."

The best way to keep crows away, Sugita advises, is to use a combination of methods and change them frequently, preferably every few days. Noise, reflective tape and balloons are just a few of the other crow-control measures currently used in agriculture areas. In cities, nets are effective in keeping crows out of garbage bags at collection sites when used properly.

"Urban crow populations grow because humans destroy their natural habitats and then provide an excellent source of food in garbage set out for collection. You aren't going to solve the crow problem in cities unless you solve the garbage problem," Sugita cautioned. "The best approach is to restore a natural balance so crows and humans can coexist."

Now that would be something to crow about.