The Vector Sum Model of Pigeon Landmark Use

Two experiments further tested a model of how pigeons use landmarks to find a location. The vector sum model (Cheng, 1988) predicts that when a landmark is shifted in one direction from its usual position, the bird's peak place of search may shift in that direction, but not in the orthogonal direction. The weight placed on a particular landmark is estimated by the extent to which the bird shifts its searching in the direction of the landmark shift. In the experiments, birds were trained to find a goal with one near landmark and one far landmark on either side of it. On occasional tests, one or both landmarks were shifted. Results showed that on the whole, the birds weighted the nearer landmark more than the farther landmark. In conformity with the predictions of the vector sum model, no bird shifted its peak place of search in the direction orthogonal to the direction of landmark shift.