Tool use and tooling in ravens ( Corvus corax ): A review and novel observations

Corvids are known for their cognitive flexibility, and many have innovated various forms of tool use. Here, we review tool use and tooling in common ravens (Corvus corax) and describe additional observations. In total, they have used tools in 10 submodes and 11 modes. Of these modes, four were observed in captivity only, four in the wild only and three in both contexts. Five of these modes constitute tooling. When they manufactured tools, it was through detachment or subtraction. The purpose of most tool use was apparent, except when they used containers to transport small amounts of food that could be held in their bill and antelingual pouch (estimated to hold at least 16.2 ml). The small number of tool-using individuals per mode and the lack of detailed descriptions limit further interpretation and generalizability. Nonetheless, ravens are likely customary tool users in three modes and show the capacity for diverse tool use, which should be examined in dedicated future experiments.