Manipulation of walnuts to facilitate opening by the great spotted woodpecker (Picoides major): is it tool use?

True tool use has been documented in some bird species, but to our knowledge, it has not been shown in woodpeckers. Here, we investigated the ability of Picoides major to open nuts of Juglans mandshurica by consistently inserting walnuts between tree branches in a specific position that facilitated nut opening. As seen in these birds, we showed that woodpeckers removed 96% of the nuts of J. mandshurica from experimental seed trays and inserted each nut in a precise position that specifically allowed nut cracking. When we inserted nuts in an alternative position, woodpeckers manipulated and repositioned nuts to allow nut opening. In contrast, when we inserted the nuts in positions preferred for nut opening, woodpeckers did not alter their position and instead opened the nuts. We suggest that the origin of this behavior, as in other forms of tool use, likely requires a higher cognitive ability in these birds.