A fascinating article from Aeon Magazine.
A crumbling concrete wall, a ramp and a vast expanse of asphalt on which identical silvery-grey sedans are slowly circling and zigzagging between traffic cones. It does not seem like much but, to urban biologists, the Kadan driving school in the Japanese city of Sendai is hallowed ground. The four of us (the biology students Minoru Chiba and Yawara Takeda, the biologist Iva Njunjić, and I) have been sitting on that crumbling wall for several hours now, hoping to observe what this place is famous for.
It was here that, in 1975, the local carrion crows (Corvus corone) discovered how to use cars as nutcrackers. The crows have a predilection for the Japanese walnut (Juglans ailantifolia) that grows abundantly in the city. The pretty nuts (a bit smaller than commercial walnuts, and with a handsome heart-shaped interior) are too tough for the crows to crack with their beaks, so for time immemorial they have been dropping them from the air onto rocks to open them. Everywhere in the city, you find parking lots strewn with the empty nutshells: the crows either drop them in flight or carry them to the tops of adjoining buildings and then throw them over the edge onto the asphalt below.
But all this flying up and down is tiring, and sometimes the nuts need to be dropped repeatedly before they split. So, at some point, these crows came up with a better idea. They would drop nuts among the wheels of slow-driving cars, and pick up the flesh after the car had passed. The behaviour started at the Kadan driving school, where there are plenty of slow-moving cars, was copied by other crows, and so spread to other places in the city where slow-moving giant nutcrackers were common, such as near sharp bends in the road, and at intersections. At such places, rather than dropping the nuts from above, the crows would station themselves by the roadside and place them more accurately on the road. Since then, the fad has also turned up in other cities in Japan.
In 1995, the zoologist Yoshiaki Nihei then at Tohoku University in Sendai made a detailed study of the behaviour. He observed how the crows would wait near a traffic light, wait for it to turn red, then step in front of the cars, place their nuts, and hop back to the curb to wait for the light to change. When the traffic had passed, they would return to the road to retrieve their quarry. His work revealed the crows’ finesse in handling their ‘tool’. For example, the birds would sometimes move a walnut a few centimetres if it took too long for it to be hit by a wheel. In one case, he even saw how a crow would walk into the path of an oncoming car, forcing it to brake, and then quickly toss a nut in front of its wheels.
These fascinating observations languished in relatively obscure Japanese scientific papers until 1997. That year, the BBC came to Sendai to film the crows for David Attenborough’s series The Life of Birds. His voice-over made them an instant hit: ‘They station themselves at pedestrian crossings … Wait for the lights to stop the traffic. Then, collect your cracked nut in safety!’
So, finding ourselves in this city with its famous urban crows, our merry band devote the day to viewing them for ourselves. Minoru and Yawara tell us that the crows’ trick is well-known in town. In fact, it is a favourite pastime to throw the crows nuts and watch them perform. So, with a bag of walnuts brought all the way from the Netherlands, we try our luck. But the crows are not cooperating. We have already spent the whole morning at traffic lights at intersections, stupidly waiting on canvas folding chairs at the mercy of the surprised stares of endless motorists but, so far, in vain. And we have now ended up at the reputed epicentre, the Kadan driving school. It is getting hot, and we’re hungry and tired. With glazed-over eyes, we stare at the heaps of nuts we have laid out at various positions on the school’s test range. The school’s students carefully avoid them, and the crows fly over without even looking down. This is what urban fieldwork is like.
Perhaps, Minoru and Yawara finally admit, it is too early in the year. The nuts are not ripe yet, the young birds have just fledged, and groups of crows are marauding the city to feast on other things, such as the ripe mulberries that are in abundance everywhere. I sigh and stare a bit more. Then, I hear a cracking noise behind me. I turn around to see that Iva has begun eating our stock of walnuts. She looks at me defiantly: ‘What? They’re not going to come anyway!’
Carrion crows do not occur only in Japan. They also exist in western Europe, where you can similarly find plenty of cars, pedestrian crossings and walnuts. And yet carrion crows in Europe somehow never learnt to exploit human automobile traffic in the Rube-Goldbergian way that they do in Japan.
Retrieved April 18, 2018 from https://aeon.co/essays/how-city-birds-evolved-to-be-smarter-than-rural-birds