Darwin Comes to Town by Menno Schilthuizen

Author:Menno Schilthuizen
Language: eng
Format: epub
Publisher: Picador

15

SELF-DOMESTICATION

A crumbling concrete wall, a ramp, and a vast expanse of tarmac on which identical silvery-gray 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 (biology students Minoru Chiba and Yawara Takeda, biologist Iva Njunjić, and I) have been sitting on that crumbling wall now for several hours, hoping to observe what this place is famous for.

It is 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), which 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 behavior 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.

A zoologist of Sendai’s Tohoku University, Yoshiaki Nihei, made a detailed study of the behavior. 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 lights to turn. When the traffic had passed, they would return onto the tarmac 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 centimeters 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.

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