Are Clark’s nutcrackers (Nucifraga columbiana) able to discriminate knowledge states of human experimenters during an object-choice task?

From the book : Evolutionary Psychology 11 issue 3 : 628-646.
Corvids and primates have been shown to possess similar cognitive adaptations, yet these animals are seldom tested using similar procedures.
Object-choice tasks, which have commonly been used to test whether an animal is able to infer the mental state of a human experimenter based on a gestural cue, provide one potential means of testing these animals using a similar paradigm.
The current study used an object-choice task to examine whether the corvid, Clark’s nutcracker (Nucifraga columbiana), is able to use a cognitive strategy to discriminate between the knowledge states of two human experimenters.
One experimenter was informed, and the other uninformed, as to the location of a food reward hidden inside one of two opaque containers.
During the Uninformed Gesture condition, the nutcrackers were given probe tests during which only the person performing as the uninformed experimenter provided a gesture.
Thus, the nutcrackers could not use the experimenter’s gesture to reliably find the food.
During the Gesture Conflict condition, the nutcrackers were presented with a cue conflict.
During probe tests, both the informed and the uninformed experimenter gestured to separate containers.
Thus, to find the food the nutcrackers had to use the gesture from the informed experimenter and refrain from using the gesture of the uninformed experimenter.
Our results showed that when the uninformed experimenter’s gesture was presented alone, the birds continued to follow the gesture even though it was not consistently predictive of the food’s location.
However, when provided with two conflicting gestures, as a group the nutcrackers responded to the gesture of the informed experimenter at above chance levels.
These results suggest that the birds had learned that the gesture was informative, perhaps by associative learning, yet when this mechanism was not reliable the nutcrackers were able to use either the human experimenters’ presence/absence during the baiting process, or possibly their knowledge states, to determine which gesture to rely upon.