Variations of behaviour of Carrion Crows Corvus corone using automobiles as nutcrackers

Abstract

We investigated the curious behaviour of Carrion Crows Corvus corone that make use of automobiles to crack walnuts. A typical sequence of the behaviour is : a crow puts a walnut in front of the automobile that is stopped by a traffic signal ; then the car run over the walnut and the crow eats the fragements of the walnut. This behaviour was frequently seen during the 21 months of the observation period and 43 occurrences of these were recorded in detail. The behaviour is found to consist of several variables : the procedure to get walnuts, the state of walnuts, the way to set walnuts on the road, time of the day, places, whether there are other crows around, how long to wait before abandoning, whether the crow tries to change the position of the walnuts, and the way the crow eats the cracked walnuts. The analyses of these variables suggest that the car-using behaviour of the crows is not accidental but rather systematic. Crows sometimes drop walnuts from more than 10 meters above the ground to crack them but some walnuts are too hard to crack by this method. We suggest the car-using behaviour is an alternative invention to crack walnuts that are too hard, or walnuts covered with pulp. Taken together, we consider the car-using beheviour of Carrion Crows to be intentional behaviour