As the season progresses, Carrion Crows Corvus corone rely less on automobiles crushing walnuts and increasingly drop walnuts to crack them open

Abstract

Carrion Crows Corvus corone crack open Manchurian Walnuts Juglans mandshurica using two techniques: by placing them on roads for automobiles to run over them, or by dropping them from a height. The hardness of the walnuts influences their choice of technique. A previous experimental study found that dropped walnuts cracked open more readily as the season progressed. If crows are aware of this, they can be expected to rely less on automobiles and more on dropping later in the winter. Our observations of crow behavior from October to January revealed that they do in fact use the dropping technique increasing as the season progresses, as predicted.