Evidence for orientation using the e-vector direction of polarised light in the sleepy lizard Tiliqua rugosa

Adult sleepy lizards (Tiliqua rugosa) were trained to orient in a predictab le direction under natural sky light in outdoor pens, When tested under cle ar skies in the late afternoon, without a view of the sun, the lizards exhi bited a symmetrical bimodal pattern of orientation with respect to the trai ned axis. Since the e-vector of polarised light provides an axial rather th an a polar cue, the bimodal orientation exhibited by the lizards is consist ent with the use of a celestial compass based on sky polarisation patterns. To confirm that the lizards could orient with respect to a polarisation pa ttern, lizards were trained in indoor pens to orient in a predictable direc tion under a linearly polarised light source, When tested in a circular are na illuminated by another polarised light source, the lizards used the e-ve ctor direction of the polarised light source to orient along the trained ax is, There was no evidence that the lizards were using any room-specific cue s or brightness patterns to orient in the training direction, These results support the hypothesis that the lizards can use the e-vector direction of polarised light in the form of a sky polarisation compass.