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Do crows reason about causes or agents? The devil is in the controls

In a recent issue of PNAS, Taylor et al. (1) claimed that New Caledonian crows can reason about hidden causal agents (HCAs). Crows first experienced three trials in the HCA condition: they saw a human enter a hide within their aviary; a stick being poked from the hide toward a foraging site; and the human leaving. In the subsequent unknown causal agent (UCA) condition, the crows only saw the poking. The animals inspected the hide less often in the first condition, prompting the authors to suggest that the crows “attributed the movement of the stick…to the agent” and that the crows inferred that the stick was unlikely to move again once the human had left. The authors encouraged future comparative studies to adopt the same methodology to uncover the evolutionary forces that led to this cognitive ability, which we agree would be an interesting endeavor. However, we suggest additional controls are critical if the results are to be diagnostic of the ability to represent causes or agency.