Angular amplitude matters: exploring the functional relationship of geometric cue use by Clark's nutcrackers (Nucifraga columbiana).

Four groups of Clark's nutcrackers (Nucifraga columbiana) learned to search for food hidden at one of two geometrically identical corners of a parallelogram-shaped enclosure. The corners of the enclosure projected either 40° and 140° angles or 60° and 120° angles. Tests using both rhomboid and rectangular enclosures examined whether birds had encoded angular amplitude and the length of walls, respectively. Cue conflict tests using a mirror-image of the training parallelogram reversed the relationship between wall length and corner angle, allowing for the examination of cue weighing. Furthermore, cue conflict tests which manipulated the angular amplitude allowed for the investigation of whether the encoding of angular information was similar among the training groups. Our results showed that nutcrackers encoded both angular amplitude and wall length. During cue conflict tests that maintained the training angular amplitudes, birds did not show a strong weighing of angular cues at a population-level but rather considerable individual differences were found. Finally, manipulating angular amplitude in the direction towards the unrewarded angle resulted in reduced weighing of angular cues whereas manipulating angular amplitude in the direction away from the unrewarded angle resulted in greater weighing of angular cues. In summary, our results support the importance of using multiple exemplars during training and testing to better understand the functional relationship between geometric cues during a spatial search task.