The use of local and global cues by clark's nutcrackers, Nucifraga columbiana

Clark's nutcrackers, Nucifraga columbiana, were studied to determine what spatial cues may be important to searching behaviour when finding a hidden goal. In the first experiment birds were trained to find seeds buried beneath wood chips on a stationary tray (following Cheng and Sherry 1992, J. comp. Psychol., 106, 331-341). The seeds were located near a glass landmark and one edge of the tray. During unrewarded test trials, the glass landmark could be in the same position as in training (control), or else moved parallel, perpendicular or diagonally with respect to the edge. Parallel movement caused the birds to shift their search, but perpendicular movement did not, suggesting that the local landmark did not influence searching in the perpendicular as much as the parallel direction. In a second experiment, the glass landmark was removed with the tray stationary or shifted. When the tray was shifted, the birds tended to search in the same place relative to global room cues as they did when the tray was not shifted. This use of global cues suggests that they may have also been important in the first experiment. In the third experiment, the tray was placed in a different position for each trial, making global cues unreliable. The birds were much more sensitive to landmark displacement in test trials, confirming the role of global cues during the first experiment. Clark's nutcrackers may be particularly sensitive to global cues in these kinds of spatial tests due to their caching behaviour.