Investigation of cognitive mechanisms and strategy on solving multiple string-pulling problems in Azure-winged magpie (Cyanopica cyanus).

String-pulling tasks are a widely used paradigm in animal cognition research. The present study tested whether ten azure-winged magpies (Cyanopica cyanus) could solve a series of multiple-strings problems with the aim of systematically investigating which rules this species uses to solve different-patterned string tasks, i.e., tasks in which subjects have to choose between two strings only one of which is connected to bait. When the subjects faced the parallel strings task (T1), five birds (C3, C5, C8, C9, and C10) were able to solve the task and acted in a goal-directed manner. Three birds (C5, C8, and C9) successfully solved the oblique parallel strings task (T3). The azure-winged magpies exhibited proximity selection in the oblique parallel strings task (C1 and C4 in T2), and the task with one string folded at a right angle (C3, C6 and C8 in T5). Several subjects also performed simple strategies in other unresolved tasks, e.g., random selection, trial-and-error learning, and side bias strategies (i.e., a certain degree of "left-handed" tendency). These results demonstrated that the azure-winged magpie possesses the potential to solve simple multiple-string tasks, although when faced with more difficult problems they could not solve them.