Wild Crows Seem to Obey 'Do Not Enter' Signs

Crows are incredibly clever birds. Some species use tools, for example. Some also recognize human faces, even "gossiping" about who's a threat and who's cool. Crows can hold long-term grudges against people they deem dangerous, or shower their allies with gifts. Oh, and they can solve puzzles on par with a 7-year-old human.

With wits like this, it's little wonder crows have adapted to live in human cities around the world. Yet despite all their uncanny displays of intelligence, a recent example from Japan is eyebrow-raising even for these famously brainy birds.

Wild crows had learned to raid a research building in Iwate Prefecture, stealing insulation to use as nest material. But as the Asahi Shimbun reports, they abruptly quit after a professor began hanging paper signs that read "crows do not enter."

The idea was suggested by a crow expert from Utsunomiya University, and has reportedly worked for the past two years. This doesn't mean the crows can read Japanese, but it may still shed light on their complex relationship with people.

Beaked bandits

The building in question is the International Coastal Research Center (ICRC), part of the University of Tokyo's Atmosphere and Ocean Research Institute in Otsuchi. The ICRC was founded in 1973 to promote marine research around the biodiverse Sanriku Coast, but its building was heavily damaged by the 2011 Great East Japan earthquake and tsunami, which flooded all three stories. Nearby houses were all destroyed, the Asahi Shimbun reports, and many residents have moved elsewhere.

Repairs later allowed temporary use of the third floor, but the first and second floors were cleared for warehouse space. While the University of Tokyo is working to rebuild the center and restart its research, that "is expected to cost a substantial amount of money and several years of time," according to the ICRC website.

The crows began their raids on the damaged building in spring 2015, according to Katsufumi Sato, a behavioral ecologist and ethology professor at the University of Tokyo. Once inside, they would find insulated pipes, tear off chunks of insulation and then fly away, leaving behind feathers and droppings as clues of their crime.

"Crows take it for their nests," Sato tells Shimbun staff writer Yusuke Hoshino.

Hoping for a simple solution, ICRC staff sought advice from Sato, who in turn asked his friend Tsutomu Takeda, an environmental scientist and crow expert at Utsunomiya University's Center for Weed and Wildlife Management. When Takeda suggested making signs that tell crows to stay out, Sato says he thought it was a joke. But he gave it a try, and crows quit raiding the ICRC "in no time at all," Hoshino writes.

Sato remained skeptical, assuming this was a temporary coincidence, but the crows stayed away throughout 2015, even though the building still had openings and still had insulation inside. He put up the paper signs again in 2016, and after another year without crow attacks, he kept up the tradition this spring. Crows can still be seen flying around nearby, Hoshino points out, but their raids seem to have ended.

As the crow spies

So what's going on? Crows can't read, but could they still somehow be getting information from the signs? As the BBC documented a decade ago, some urban crows in Japan have learned to capitalize on traffic lights, dropping hard-to-crack nuts into traffic so cars will run over them, then waiting for the light to turn red so they can safely swoop down and grab their prize. That's impressive, albeit not quite the same.

Takeda offers a different explanation. The crows aren't responding to the signs at all, he says; they're responding to people's responses. People might normally ignore common urban wildlife like crows, but these warnings — while ostensibly directed at crows themselves — draw human attention to the birds. As ICRC staff, students and visitors see the strange signs, they often look up at the crows and even point at them.

"People gaze up at the sky [looking for crows], you know," Takeda says.

For clever birds that pay close attention to people, that's apparently eerie enough to make the ICRC seem unsafe. It's worth noting this is anecdotal, not a scientific study, and there may be another reason why the crows stopped their raids. But given how closely it correlated with the new signs, and how perceptive crows can be, Takeda's plan is being credited with cheaply and harmlessly keeping the birds at bay.

If nothing else, this is a reminder to appreciate these intelligent birds living all around us, even in cities we built for ourselves. But since crows are sometimes a little too good at exploiting urban environments, it's also a helpful reminder of how much a dirty look can accomplish. Sato, now a believer in Takeda's unorthodox strategy, hopes more people will come to the ICRC and gawk at the local crows.

"The effectiveness will increase if there are more people looking at the crows," Sato says. "So please feel free to visit us!"