Geometric and Feature Encoding of Discrete Landmark Arrays in Clark's Nutcrackers: What External Cues Aid in Avian Navigation and Heading Determination?
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Investigating whether animals use geometry of the environment to reorient involves examining aspects of the environment are available for encoding geometrical information. Cheng (1986) demonstrated that overall geometric shape of the environment can be encoded to aid in navigation, but few have asked this question using discrete landmarks. If animals can use geometric information to reorient, it would be advantageous to use the geometry not only of continuous surfaces but also the configuration of discrete objects. In this study, two groups of Clark's nutcrackers, Nucifraga columbiana, a highly spatial bird, were trained to locate a hidden goal based on the configuration of four discrete landmarks. One group was given an array consisting of four distinct landmarks, each differing in color and shape. The second group was shown an array consisting of four identical landmarks. Presentations of the landmark array differed in orientation for each trial (but the relationships between the landmarks remained stable). We performed several landmark transformation tests to examine how aspects of the landmark array are used. Understanding if nutcrackers can conjoin geometric and feature information presented using a discrete landmark array, as well as the relationship between both types of information, is important to understand avian orientation and navigation not only in laboratory based environments but in natural situations. Our initial results showed that the group given distinct landmarks (the Feature group) learned to locate the hidden goal with high accuracy using the feature and absolute geometric information of the array, but encoding relative geometry to orient fell to chance. The group given only identical landmarks (the Geometry group) failed to complete the shaping procedures and advance to testing. More test trials will be run to examine further how Nucifraga columbiana learns the geometrically similar landmark array.