Carrion crows were observed using roads as a tool for opening walnuts. Instead of cracking every shell themselves, the birds sometimes placed walnuts on the road in front of cars stopped at traffic signals. When a vehicle moved over the walnut, the crow returned to eat the broken pieces. The behaviour was not based on a single observation. According to research published in the Japanese Journal of Ornithology, titled ‘Variations of behaviour of Carrion Crows Corvus corone using automobiles as nutcrackers’, recorded 43 occurrences in detail during a 21- month observation period. The study found that the behaviour involved several variables, from how walnuts were placed to how long the birds waited. The researchers suggested that the car-using behaviour was systematic rather than accidental and considered it an intentional way of cracking walnuts that were difficult to open. The observations offer a look at how wild birds can make use of human infrastructure while solving a feeding problem.
How carrion crows used cars to crack walnuts
The sequence was clear. A carrion crow took a walnut and placed it in front of an automobile stopped at a traffic signal. The vehicle ran over the walnut, breaking its shell. After the car passed, the crow returned and ate the fragments. The research author Yoshiaki Nihei recorded this behaviour repeatedly during 21 months, with 43 occurrences documented. The study noted that crows did not always behave the same way. Their actions varied according to how they took walnuts, the condition of the walnuts, where they placed them, the time of day, and the presence of other crows. It also varied how long they waited and whether they repositioned walnuts before retrieving the cracked pieces from the road.
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Why the behaviour appeared systematic rather than accidental
The observations suggested that the crows were using traffic purposely rather than leaving walnuts on the road by chance. The researchers examined parts of the behaviour, including how the birds positioned walnuts, how long they waited for vehicles, and whether they changed a walnut’s position. They also considered how the birds behaved when other crows were nearby and how they consumed cracked walnut pieces. These variations supported the study’s argument that the behaviour was systematic. The research paper did not describe every crow behaving identically. Instead, it identified a recurring sequence with elements. Taken together, those observations led the researchers to regard the car-using behaviour as intentional for obtaining walnut fragments after the shells had been cracked.
Crows had another way to crack hard walnuts
The paper described another way carrion crows can crack walnuts. Birds dropped walnuts from heights above 10 metres. This could break some walnuts, but certain walnuts were too hard to crack by dropping them. The car-based method provided another option for difficult walnuts. Nihei suggested that using automobiles could be an alternative method for walnuts that were too hard to crack by dropping or were still covered with pulp. This does not mean that every walnut requires a car. The observations suggested that crows had more than one way to deal with walnuts. Their use of passing vehicles formed part of a broader pattern of nutcracking behaviour documented in the study.
What the 21-month observations revealed about the crows
What makes the observations notable is repetition and flexibility. The crows used traffic and then adjusted parts of the process depending on circumstances. It could vary where a walnut was placed, whether they changed its position, and how long they waited. The study recorded differences in the way the birds ate the cracked walnuts.They examined repeated occurrences and several parts of the sequence over 21 months. On the basis of those observations, Nihei concluded that the car-using behaviour was systematic and considered it intentional.