Object permanence in rooks (Corvus frugilegus): Individual differences and behavioral considerations.

Piagetian object permanence (OP) refers to the ability to know that an object continues to exist when out of sight: In humans, it develops in six stages. Species of great apes, other mammals, and birds (parrots, corvids, and pigeons) have been shown to possess partial or full OP, which is a prerequisite for more complex physical cognition abilities they may possess. In birds, the greatest variation is in Stage 6 (invisible displacements) and in "A-not-B" errors-incorrectly persevering in searching an empty location rewarded previously. Caching abilities have been invoked as holding explanatory power over results in corvids, for which this error is sometimes completely absent. The rook (Corvus frugilegus), a cognitively advanced, social, caching corvid, has not yet been studied for OP. This study applies tasks of one OP scale commonly adapted for nonhuman animals, Uzgiris and Hunt's Scale 1, as well as later-conceived tasks 16 and S, to a sample of adult, captive rooks. One rook demonstrated full OP (Stage 6b, multiple invisible displacements), whereas other individuals varied, attaining between Stages 5a (single visible displacements) and 6a (single invisible displacements). Like some corvids, a few made transient "A-not-B" errors. Behavioral considerations potentially underlying observed individual variation in results in rooks, including dominance, neophobia, past experiences, and individual idiosyncrasies, are examined. Rooks, like other corvids, possess well-developed OP abilities, and these results support the idea that exertion of executive control is required to avoid "A-not-B" errors, rather than caching abilities or developmental age, as previously suggested.