Clark's nutcrackers (Nucifraga columbiana) and the effects of goal--landmark distance on overshadowing.

Three groups of Clark's nutcrackers (Nucifraga columbiana) were trained to find a goal location defined by an array of 4 landmarks that varied in goal--landmark distance. The arrays for each group differed in the distance of the closest landmark and contained goal--landmark distances that were common across groups, allowing for the examination of the effects of both relative and absolute goal--landmark distance on encoding of a landmark array. All 3 groups readily learned the task and were subsequently tested in probe tests with only single landmarks from the array available. Search error in tests with single landmarks was compared both within and across groups. Results demonstrated that both relative and absolute goal-landmark distances are important in spatial search.