Vice-anvil use in nut processing by two Corvus species

Abstract

Woodpeckers and certain passerine species secure encased food in the environment in various ways to facilitate the extraction of the contents with their bills. They do this by securing the food items in locations such as crevices and holes, newly defined in this paper as ‘vice-anvils’. Here I report that free-living New Caledonian crows (Corvus moneduloides) and rooks (Corvus frugilegus, in New Zealand) also use vice-anvils to process candlenuts and walnuts, respectively. New Caledonian crows placed candlenut sections in vice-anvils to aid kernel extraction, after the candlenuts had been dropped onto an anvil to break them open. In contrast, rooks used vice-anvils to secure walnuts while they broke the shell with their bills. Long-term use by rooks of a vice-anvil in a tree had produced a ‘purpose-made’ nut-cracking site. My findings extend the persistent use of specific vice-anvils to Corvus species and further demonstrate their innovative and flexible foraging behaviour.