On 2017 Oct 02, Serge Ahmed commented:

This article reports an interesting set of experiments showing that ravens repeatedly choose among a set of different objects, an object that will prove several minutes or hours later to be useful to obtain food. The authors interpret this preference as evidence that ravens would be able to plan for the future. However, since the preferred object was repeatedly and selectively paired with food reward during initial training, one cannot definitively rule out the involvement of non-planning processes. For instance, ravens could prefer the would-be useful object, not because they anticipate its future utility, as hypothesized by the authors, but merely because they attach more affective and/or motivational value to the object due to its past selective association with food reward. To rule out this associative mechanism, it is important to add a control condition where, all else being equal, choice of the previously food-paired object is not followed by an opportunity to use it to obtain food (for a similar criticism and a specific example of a control condition, see: Redshaw et al. https://www.ncbi.nlm.nih.gov/pubmed/28927634).

On 2017 Oct 02, Serge Ahmed commented:

This article reports an interesting set of experiments showing that ravens repeatedly choose among a set of different objects, an object that will prove several minutes or hours later to be useful to obtain food. The authors interpret this preference as evidence that ravens would be able to plan for the future. However, since the preferred object was repeatedly and selectively paired with food reward during initial training, one cannot definitively rule out the involvement of non-planning processes. For instance, ravens could prefer the would-be useful object, not because they anticipate its future utility, as hypothesized by the authors, but merely because they attach more affective and/or motivational value to the object due to its past selective association with food reward. To rule out this associative mechanism, it is important to add a control condition where, all else being equal, choice of the previously food-paired object is not followed by an opportunity to use it to obtain food (for a similar criticism and a specific example of a control condition, see: Redshaw et al. https://www.ncbi.nlm.nih.gov/pubmed/28927634).